AGRIC. 
LIBRARY 


DISEASES    OF    TRUCK    CROPS 

AND   THEIR    CONTROL 


OTHER  WORKS 
BY  THE  SAME  AUTHOR 

The  Culture  and  Diseases  of 
the  Sweet  Pea  -  $2.00  net. 

Profusely  Illustrated 

Diseases  of  Greenhouse  Plants 

(In  Preparation) 


Diseases  of  the  Sweet  Potato 

(In  Preparation) 


E.  P.  DUTTON  &  COMPANY 
NEW  YORK 


DISEASES  OF  TRUCK  CROPS 

AND  THEIR  CONTROL 


BY 


J.  J.  TAUBENHAUS,  PH.D. 

Plant  Pathologist  and  Physiologist  to  the  Agricultural  and  Mechanical 

College  of  Texas 
Author  of  "  Culture  and  Diseases  of  the  Sweet  Pea  " 


NEW  YORK 

E.  P.  BUTTON  &  COMPANY 
681  FIFTH  AVENUE 


V 

tf 


Copyright,  1918 
By   E.  P.  DUTTON  &  COMPANY 


PRINTED  IN  THE  UNITED  STATES  OF  AMERICA 


TO  MY   FRIEND 

B.    KACZER 


425501 


PREFACE 

THE  world  never  has  faced  a  greater  shortage  of 
food  than  to-day.  War's  destructive  agencies  have 
added  themselves  to  our  old  invisible  foes,  namely 
parasitic  and  disease-producing  bacteria  and  fungi. 

More  than  half  of  our  diet  is  made  up  of  vege- 
tables. They  furnish  the  necessary  food  bulk  which 
the  body  requires,  supply  important  nutritive  ele- 
ments, and  act  as  stimulants  to  a  better  blood  circu- 
lation. According  to  the  Thirteenth  Census  of  the 
United  States  the  area  devoted  to  truck  crops  in  the 
United  States  in  1909  was  estimated  at  7,436,551 
acres.  The  total  money  value  of  the  truck  crops 
grown  on  this  acreage  was  estimated  at  $301,104,144. 
The  crops  thus  estimated  included  asparagus,  beans 
(green),  beans  (dry),  beets,  cabbage,  cauliflower, 
corn  (pop  and  sweet),  cantaloups,  carrots,  celery, 
chicory,  cucumbers,  egg  plant,  horse-radish,  kale, 
lettuce,  mint,  okra,  onions,  parsley,  parsnip,  peas 
(green),  peas  (dry),  peppers,  pumpkin,  radish, 
rhubarb,  rutabagas,  spinach,  sprouts,  squash,  sun- 
flower, sweet  potato  and  yam,  tomatoes,  turnips,  and 
watermelon. 

We  scarcely  realize  the  large  sums  of  money  which 
the  trucker  loses  annually  from  specific  plant  dis- 
eases, because  there  are  few  available  data  as  to 

vii 


viii  Preface 

the  money  losses.  But  as  an  example,  the  following 
figures,  kindly  given  to  the  writer  by  Professor  R.  P. 
Haskell,  Pathological  Inspector  of  the  United  States 
Department  of  Agriculture,  will  be  of  compelling 
interest. 

"  Potato  Diseases. — It  is  estimated  that  the  State 
of  New  York  lost  in  1915,  principally  from  late 
blight,  about  $20,000,000.  This  outbreak  was  wide- 
spread in  the  northern  States  and  reduced  the  yields 
as  shown  below,  in  comparison  with  1914.  Other 
conditions  than  disease  were  relatively  equal : 

Maine  10,000,000  bu. 

New  Hampshire  1,200,000  " 

Vermont  1,600,000  " 

New  York  30,000,000  " 

Pennsylvania  8,000,000  " 

Michigan  23,000,000   " 

Wisconsin  11,700,000  " 

"It  is  estimated  that  the  market  value  of  the 
potato  crop  in  Aroostock  County,  Maine,  in  1915 
was  reduced  about  10%,  or  $1,078,000,  on  account  of 
the  occurrence  of  the  powdery  scab  disease.  In 
some  sections  the  reduction  amounted  to  as  much 
as  50%. 

"It  is  estimated  that  50%  of  the  potato  crop  in 
Idaho  was  injured  by  diseases  last  year  and  from  10% 
to  20%  rendered  wholly  unsalable.  The  total  an- 
nual loss  in  this  State  is  estimated  at  $196,000. 

"Sweet-Potato  Diseases. — It  is  estimated  that  the 
annual  loss  due  to  sweet-potato  diseases  in  the 


Preface  ix 

United  States  is  approximately  $10,000,000.  About 
$750,000  of  this  loss  may  be  attributed  to  stem  rot, 
the  other  important  diseases  being  black  rot,  foot 
rot,  and  storage  rots. 

"Asparagus  Rust. — Asparagus  rust  has  practically 
destroyed  all  of  the  original  plantings  of  asparagus 
and  driven  the  old  varieties  out  of  cultivation.  These 
have  now  been  replaced  by  partially  resistant  kinds 
and  the  new  strain  bred  by  this  Department  is  almost 
wholly  resistant,  so  that  in  the  near  future  these 
losses  will  be  eliminated.  Tests  of  some  of  the  new 
rust-resisting  strains  in  1915  showed  gains  over  the 
standard  varieties  amounting  to  more  than  $200 
per  acre. 

"  Cowpea  Diseases. — It  is  estimated  that  the  an- 
nual saving  as  a  result  of  the  introduction  of  wilt 
and  root-knot  resistant  cow-peas  is  $3,000,000." 

A  conservative  estimate  of  the  money  loss  from 
diseases  would  be  about  20%  of  the  total  value  of 
the  truck  crops  grown  in  the  United  States.  Accord- 
ing to  the  estimate  given  on  page  vii,  the  total  value  of 
the  truck  crop  in  the  United  States  in  1909  amounted 
to  the  sum  of  $301,104,144.  If  20%  of  this  was  lost 
through  damage  from  diseases,  it  will  be  seen  that 
in  1909  the  American  truckers  lost  $60,220,828. 
This  does  not  include  the  large  losses  from  insect 
pests,  nor  losses  incurred  in  storing,  or  in  shipping 
truck  produce. 

It  is  no  exaggeration  to  state  that  if  our  present 
knowledge  of  Plant  Pathology  were  made  use  of  by 
truck  farmers,  nearly  80%  of  this  loss  could  be 


x  Preface 

prevented.  Can  any  one  say  that  such  a  saving 
would  be  insignificant,  untimely,  or  unpatriotic? 

The  present  work  has  been  prepared  with  the  aim 
of  stimulating  more  research  in  truck-crop  diseases, 
and  also  of  assisting  the  trucker  to  make  use  of  our 
present  knowledge,  in  order  to  prevent  avoidable 
losses,  increase  the  trucker's  profits,  and  assure  a 
greater  food  supply.  The  writer  seriously  solicits 
suggestions  or  criticisms  on  his  work. 

Acknowledgments  are  due  to  Dr.  and  Mrs.  D.  de 
Sola  Pool,  of  New  York  City,  for  the  inspiration,  the 
encouragement,  and  the  valuable  assistance  rendered 
in  the  preparation  of  the  manuscript,  and  later  in 
reading  and  criticizing  it.  To  Dr.  E.  A.  Bessey  of 
the  Michigan  Agricultural  College,  and  to  Dr.  Mel. 
T.  Cook  of  Rutgers  College,  the  author  owes  hearty 
thanks  for  the  careful  reading  and  the  valuable 
suggestions  and  criticisms  which  they  have  given  this 
work.  Acknowledgments  are  also  due  to  Dr.  G. 
H.  Coons  of  the  Michigan  Agricultural  College,  to 
Prof.  P.  B.  Paddock  and  to  Mr.  W.  T.  Brink  of  the 
Texas  Agricultural  Experimental  Station  for  reading 
the  manuscript  and  proof.  Grateful  appreciation  is 
likewise  due  to  Dr.  I.  Adlerblum  of  the  Metropolitan 
Life  Insurance  Co.  of  New  York  City  for  criticizing 
the  manuscript  and  proofs. 

For  the  use  of  illustrations  the  author  is  indebted : 
to  Dr.  G.  P.  Clinton;  to  Dr.  Mel  T.  Cook;  to  Drs. 
G.  H.  Coons  and  E.  Levin;  to  Dr.  H.  A.  Edson;  to 
Dr.  B.  B.  Higgins;  to  Prof.  H.  S.  Jackson;  to  Dr.  L. 
R.  Jones;  to  Dr,  T.  F.  Manns;  to  Prof.  A.  V.  Osmun; 


Preface  xi 

to  Prof.  F.  B.  Paddock;  to  Prof.  W.  G.  Sackett;  to 
Prof.  A.  D.  Selby;  to  Prof.  R.  E.  Smith;  to  Prof.  H. 
E.  Stevens;  to  Prof.  J.  A.  Stevenson;  to  Prof.  D.  B. 
Swingle;  to  Prof.  DeVault  and  to  Dr.  F.  A.  Wolf. 

Last,  but  not  least,  grateful  acknowledgments  are 
due  my  wife  Esther  Michla  Taubenhaus,  whose  de- 
votion to  art  and  science,  and  whose  inspiration  made 
this  work  possible. 


J.  J.  TAUBENHAUS 


COLLEGE  STATION,  TEXAS 
January  22,  ipi8. 


PREFATORY  NOTE 

WITH  the  greater  specialization  along  all  lines  of 
industry  the  problems  that  confront  such  a  specialist 
as  the  author  of  this  book  are  felt  more  keenly  and 
the  necessary  remedies  are  more  fully  appreciated. 
So  there  has  grown  up  in  the  last  few  decades  in 
this  country  a  body  of  agricultural  experts,  the 
truck  growers,  who  have  found,  as  they  have  con- 
centrated their  attention  more  and  more  inten- 
sively upon  a  limited  number  of  crops,  that  they 
are  paying  a  great  tax  in  the  shape  of  losses  due 
to  diseases.  Probably,  in  fact  we  know  that  very 
often  it  certainly  is  the  case,  similar  losses  are 
suffered  by  general  farmers,  but  with  their  large 
plantings  and  less  intensive  culture  these  losses  are 
not  appreciated  as  they  are  by  the  truck  grower. 
Other  factors,  too,  enter  in.  In  general  the  truck 
crops  occupy  land  near  cities  or  which  from  its 
adaptability  to  special  crops  or  from  its  accessibility 
to  markets  is  accordingly  more  valuable  than  ordinary 
farm  lands.  Furthermore,  the  crops  themselves 
have  a  greater  monetary  worth  than  the  staple 
crops.  Both  these  factors  make  the  losses  by  plant 
diseases  much  more  keenly  felt.  With  this  recogni- 
tion of  the  losses  incurred  has  arisen  a  demand  for 

xiii 


xiv  Prefatory  Note 

help  in  the  prevention  of  the  diseases  responsible 
for  the  damage.  So  plant  pathologists  have  had  to 
direct  their  attention  to  diseases  of  truck  crops. 
The  present  book  is  an  attempt  by  such  a  pathologist 
who  has  specialized  along  this  line  to  meet  the  de- 
mand for  help  in  the  way  of  giving  information  as 
to  the  diseases  occurring  on  truck  crops  and,  so  far  as 
it  is  possible,  telling  how  these  losses  may  be  pre- 
vented or  at  least  reduced. 

The  last  quarter  century  has  seen  a  marvelous 
development  of  that  division  of  the  science  of  Botany 
that  is  devoted  to  the  study  of  plant  diseases,  Plant 
Pathology.  As  each  crop  has  been  given  greater 
attention  the  number  of  diseases  found  to  occur 
upon  it  has  been  amazing.  Plants  nearly  related 
to  each  other  may  have  some  of  their  diseases  in 
common,  but  even  with  very  closely  related  species 
some  of  the  troubles  affecting  them  will  be  different. 
When  we  now  consider  the  large  number  of  crop 
plants  that  are  the  subject  of  intensive  culture  as 
truck  crops,  and  note,  furthermore,  that  they  re- 
present the  most  diverse  families  of  plants,  it  is  not 
to  be  wondered  at  that  the  number  of  organisms 
causing  diseases  of  truck  crops  is  a  large  one.  The 
author  by  grouping  the  crop  plants  together  by  their 
botanical  affinities  has  taken  full  advantage  of  the 
fact  that  nearly  related  plants  may  suffer  from  some 
of  the  same  diseases  and  thus  has  made  it  possible  in 
some  cases  to  consider  such  diseases  only  once  for 
several  different,  but  closely  related,  crops. 

Considerable  attention  is  directed  to  the  symptoms 


Prefatory  Note  xv 

by  which  the  various  diseases  may  be  distinguished. 
These  descriptions  are  made  in  non-technical  lan- 
guage so  that  the  practical  grower  can  understand 
them  and  recognize  the  diseases  in  question.  Besides 
this  the  methods  of  control  are  also  described  in  popu- 
lar terms.  The  author's  long  study  of  the  subject  has 
made  it  possible  for  him  to  approach  this  part  of  the 
work  from  the  standpoint  of  the  grower,  so  that  as 
far  as  possible  the  remedies  or  preventive  measures 
recommended  are  those  with  which  he  has  practical 
experience.  Occasionally  it  is  impossible  to  recom- 
mend a  remedy  since  sometimes  a  disease  is  of  such  a 
nature  that  by  the  time  it  becomes  apparent  the 
damage  is  done.  But  even  in  such  cases  directions 
are  given  which  will  reduce  the  loss  or  at  least 
permit  its  avoidance  another  season.  The  discus- 
sions as  to  the  cause  of  the  disease  are  unavoidably 
given  in  somewhat  more  technical  form  from  the 
very  nature  of  the  case,  especially  where  it  is  the 
question  of  diseases  caused  by  fungi  or  bacteria 
for  which  brief  scientific  characterizations  are  neces- 
sary. These  technical  discussions  are  essential  for 
pathologist s  and  other  students  of  the  subject  so 
that  the  book  will  be  appreciated  by  Experiment 
Station  workers,  Extension  Specialists,  college  stu- 
dents, and  others,  as  well  as  by  the  truck  growers 
themselves  for  whom  the  book  is  primarily  intended. 

ERNST  A.  BESSEY, 

Professor  of  Botany, 

Michigan  Agricultural  College. 


PAGE 


CONTENTS 
PART  I 

CHAPTER  I 

T*  TV  T  JfAUS 

IHE  NORMAL  SOIL  AND  ITS  REQUIREMENTS        .        3 

CHAPTER  II 
SICK  SOILS  NOT  INFLUENCED  BY  PARASITES         .       23 

CHAPTER  III 

SOIL  SICKNESS  DUE  TO  THE  PRESENCE  OF  PARA- 
SITES HARMFUL  TO  PLANTS         .  4! 

CHAPTER  IV 
METHODS  OF  TREATING  SICK  SOILS    ...      53 

PART  II 

CHAPTER  V 

THE  HEALTHY  HOST  AND  ITS  REQUIREMENTS        .       63 

CHAPTER  VI 
CAUSES  OF  DISEASES  IN  CROPS        .         .         .71 

A.  Diseases  of  a  Mechanical  Nature 

B.  Diseases  Due  to  Physiological  Causes 
c.  Diseases  of  Unknown  Origin 


XVll 


xviii  Contents 

PAGE 

D.  Diseases  Due  to  Parasitic  Bacteria  or  Fungi 

E.  Diseases  Induced  by  Parasitic  Flowering 

Plants 

CHAPTER  VII 
POOR  SEED 92 

PART  III 
SPECIFIC  DISEASES  OF  TRUCK  CROPS 

CHAPTER  VIII 

FAMILY  AGARICACE^:          .         .         .  .103 

Diseases  of  the  Mushroom 

CHAPTER  IX 

FAMILY  ARALIACE.E  .         .         .        .        .     108 

Diseases  of  the  Ginseng 

CHAPTER  X 

FAMILY  CHENOPODIACE^E 116 

Diseases  of  the  Beet 
Diseases  of  the  Spinach 

CHAPTER  XI 

FAMILY  COMPOSITE 137 

Diseases  of  the  Artichoke  (Jerusalem) 
Diseases  of  the  Artichoke  (Globe) 
Diseases  of  the  Lettuce 
Diseases  of  the  Salsify 
Diseases  of  the  Sunflower 


Contents  xix 

CHAPTER  XII 

PAGE 

FAMILY  CONVOLVULACE^E    .         .         .         .         .151 

Diseases  of  the  Sweet  Potato 

CHAPTER  XIII 
FAMILY  CRUCIFEILE  .         ."  .         .         .     i%$ 

Diseases  of  the  Cabbage 
Diseases  of  the  Cauliflower 
Diseases  of  the  Horse  Radish 
Diseases  of  the  Kale 
Diseases  of  the  Mustard 
Diseases  of  the  Radish 
Diseases  of  the  Turnip 

CHAPTER  XIV 

FAMILY  CUCURBITACLE        .         .         .         .         .218 
Diseases  of  the  Cantaloupe 
Diseases  of  the  Cucumber 
Diseases  of  the  Citron 
Diseases  of  the  Squash 
Diseases  of  the  Watermelon 

CHAPTER  XV 

FAMILY  GRAMINE.E    .         §      '  .         .         .          .     250 

Diseases  of  the  Sweet  Corn 

CHAPTER  XVI 

FAMILY  LABIATE       .  ,        .         .         .     255 

Diseases  of  the  Balm 
Diseases  of  the  Catnip 
Diseases  of  the  Horehound 


xx  Contents 


Diseases  of  the  Mint 
Diseases  of  the  Peppermint 

CHAPTER  XVII 

FAMILY  LEGUMINOS^E  .         •         •     259 

Diseases  of  the  Bean 
Diseases  of  the  Lima  Bean 
Diseases  of  the  Cow  Pea 
Diseases  of  the  Garden  Pea 

CHAPTER  XVIII 

FAMILY  LILIACE.E      .         .  •     279 

Diseases  of  the  Asparagus 
Diseases  of  the  Chive 
Diseases  of  the  Onion 

CHAPTER  XIX 

FAMILY  MALVACEAE   .  •     295 

Diseases  of  the  Okra 

CHAPTER  XX 

FAMILY  PORTULACACE^:      .  -     299 

Diseases  of  the  Purslane 

CHAPTER  XXI 

FAMILY  SOLANACE.E  .  .300 

Diseases  of  the  Egg  Plant 
Diseases  of  the  Pepper 
Diseases  of  the  Potato 
Diseases  of  the  Tomato 


Contents  xxi 

CHAPTER  XXII 

PAGE 

FAMILY  UMBELLIFER^E 354 

Diseases  of  the  Carrot 
Diseases  of  the  Celery 
Diseases  of  the  Parsley 
Diseases  of  the  Parsnip 
Weeds 

PART   IV 

CHAPTER  XXIII 
METHODS  OF  CONTROL 361 

CHAPTER  XXIV 
CONTROL  OF  INSECT  PESTS  BY  NATURAL  FACTORS    375 

CHAPTER  XXV 
TREATMENT  OF  FENCE  POSTS     .         .         .         .378 

GLOSSARY 381 

INDEX 387 


ILLUSTRATIONS 

FIG.  PAGB 

1.  BACTERIA          ......  4 

2.  STRUCTURE  OF  FUNGI         .         .         .         .11 

3.  NITRE-SICK  BEET  FIELD,  SHOWING  BARREN 

SPOTS 25 

4.  EFFECT  OF  LIME        .         .         .         .         .  27 

5.  PYTHIUM  DEBARYANUM       .         .         .         .  43 

6.  RHIZOCTONIA 45 

7.  FUSARIUM  WILT         .         .         .         .         -  47 

8.  NEMATODE  ROOT  KNOT      ....  49 

9.  INVERTED   PAN  FOR   STEAM   STERILIZATION  55 

10.  SURFACE    WATERING,    SHOWING    PORTABLE 

SPRAY  EQUIPMENT  USED  IN  GARDENS  ABOUT 

COLD  FRAMES  AND  HOTBEDS            .         .  55 

11.  WATERMELON  SLICE  SHOWING  HAIL  INJURY  74 

12.  LIGHTNING     INJURY     IN     POTATO     FIELD. 

DROUGHT  INJURY  OF  SWEET  CORN          .  78 

13.  MALNUTRITION,  SHOWING  A  CABBAGE  LEAF 

AFFECTED  BY  THE  DISEASE     .         .         .81 

14.  BLOSSOM  DROP 83 


xxiv  Illustrations 

FIG.  PAGE 

15.  MOSAIC 84 

1 6.  BEAN  SEEDS  AFFECTED  WITH  ANTHRACNOSE, 

Colletotrichum  lindemuthianum  ...       84 

17.  DODDER 90 

18.  MYCOGONE  DISEASE  OF  MUSHROOMS   .         .     105 

19.  GINSENG  DISEASES 109 

20.  BEET  DISEASES          .         .         .         .         .119 

21.  SPINACH  DISEASES 131 

22.  LETTUCE  DROP  .....     143 

23.  LETTUCE  DISEASES 144 

24.  SOUTHERN  BLIGHT  OF  THE  SALSIFY     .         .     148 

25.  SWEET  POTATO  DISEASES  .         .         .         .152 

26.  SWEET  POTATO  DISEASES  .         .         .  159 

27.  SWEET  POTATO  DISEASES  ....     167 

28.  SWEET  POTATO  DISEASES  .         .         .         .170 

29.  SWEET  POTATO  STORAGE  HOUSES        .         .     183 

30.  CABBAGE  DISEASES    .         .         .         . .       .187 

31.  CABBAGE  DISEASES    .         .  .         .     196 

32.  CABBAGE  DISEASES 198 

33.  DISEASES  OF  THE  CAULIFLOWER  AND  RADISH     202 

34.  CERCOSPORA  LEAF  SPOT  OF  HORSE-RADISH   .     207 

35.  RADISH  DISEASES 210 


Illustrations  xxv 

OTG.  PAGE 

36.  TURNIP  DISEASES      .        .        .        .        .215 

37.  TURNIP  DISEASES 217 

38.  CANTALOUP  DISEASES         .         .         .        .     221 

39.  RESISTANT  CANTALOUP  STRAIN  .         .         .     228 

40.  CUCUMBER  DISEASES 230 

41.  SQUASH  DISEASES 235 

42.  WATERMELON  DISEASES     ....     239 

43.  WATERMELON  ANTHRACNOSE       .         .         .241 

44.  WATERMELON  DISEASES     .  .         .     244 

45.  SWEET  CORN  DISEASES      .         .         .         .251 

46.  BEAN  DISEASES         .....     260 

47.  BEAN  DISEASES         .....     262 

48.  DISEASES  OF  LIMA  BEAN  ....     267 

49.  BEAN  DISEASES 269 

50.  DISEASES  OF  THE  Cow  PEA       .         .         .     272 

51.  DISEASES  OF  THE  GARDEN  PEA  AND  BEAN.     274 

52.  ASPARAGUS  DISEASES         ....     280 

53.  ONION  DISEASES 285 

54.  ONION  DISEASES 286 

55.  DISEASES  OF  THE  OKRA     .         .        .         .296 

56.  EGGPLANT  DISEASES  ....     302 

57.  DISEASES  OF  THE  PEPPER  .        .         .    305 


xxvi  Illustrations 

FIG.  PAGE 

58.  POTATO  DISEASES 308 

59.  DISEASES  OF  THE  POTATO           .         .         •  3J4 

60.  POX  OR  PIT  OF  THE  WHITE  POTATO,  SHOWING 

DIFFERENT  STAGES  OF  INFECTION    .         .315 

61.  POTATO  DISEASES      .         .         .                  .  322 

62.  POTATO  DISEASES      .         .         .                  .  325 

63.  POTATO  DISEASES      .         .         .         .         •  331 

64.  TOMATO  DISEASES 34° 

65.  TOMATO  DISEASES      ...                 .  346 

66.  TOMATO  DISEASES      .         .         .         .         .  347 

67.  TOMATO  DISEASES 35 1 

68.  SLEEPING  SICKNESS  OF  TOMATO           .         .  352 

69.  CELERY  DISEASES 356 

70.  CELERY  DISEASES 357 

71.  SPRAY  MACHINERY    ...                 .  372 

72.  PARASITIZED  INSECTS.   TREATMENT  OF  FENCE 

POSTS    .                  376 


INTRODUCTION 

THE  present  world  crisis  has  suddenly  transposed 
the  farmer  from  his  former  modest  and  humble  posi- 
tion into  the  ranks  of  our  foremost  national  figures. 
To-day  the  services  of  the  tiller  of  the  land  are  at 
a  premium.  The  heroes  of  the  day  are  not  only 
those  who  can  shoulder  a  gun  at  the  front,  but  also 
those  who  can  produce  the  food  necessary  to  feed  the 
great  civil  and  military  armies  in  the  field  and  at 
home.  It  is  to  the  credit  of  the  American  people 
that  they  have  realized  that  intelligent  farming  re- 
quires as  much  skill,  thought,  and  energy  as  is  re- 
quired to  build  up  industries  or  to  formulate  laws  of 
government. 

Of  the  many  phases  of  agriculture,  trucking  be- 
longs to  the  highest  forms  of  intensified  farming. 
Whether  it  is  conducted  on  a  large  or  on  a  small 
scale,  it  requires  a  thorough  knowledge  of  plant  life. 
An  intelligent  understanding  of  crop  rotation  is 
essential  for  success.  Someone  has  well  said  that 
the  farmer  may  be  judged  intellectually  by  the  system 
of  rotation  which  he  practices.  Great  skill  is  also 
required  to  keep  the  land  in  a  state  of  production 
during  the  greater  part  of  the  year.  This  is  espe- 
cially true  for  our  Southern  States.  As  a  whole, 


xxviii  Introduction 

therefore,  successful  truckers  must  be  a  highly  intel- 
ligent class  of  agriculturists. 

In  trucking,  as  in  all  intensive  farming,  the  aim  is 
to  produce  superior  crops,  embodying  both  high 
yield  and  good  quality.  This  can  be  made  possible 
only  through  intensive  breeding  and  culture.  Un- 
fortunately, however,  improvement  in  quality  and 
yield  is  often  accompanied  by  a  loss  of  natural 
vigor  and  of  power  of  resistance  to  disease.  The 
great  problem  of  the  trucker  is  twofold — that  of 
striving  for  quantity  and  quality,  while  protecting 
his  crops  from  disease.  This  latter  phase  has  gener- 
ally been  overlooked.  We  all  realize  to-day  that  it 
is  necessary  not  only  to  produce  two  blades  of  grass 
where  one  grew  before,  as  Dean  Swift  declared,  but 
also  to  conserve  it  during  growth  and  prevent  it  from 
being  carried  off  by  various  diseases.  The  great  fam- 
ine in  Ireland  in  1844  resulted  from  an  epidemic  of 
late  blight  which  destroyed  the  potato  crop.  Such  a 
condition  could  hardly  occur  to-day,  because  we  now 
have  a  better  knowledge  of  plant  life,  the  causes  which 
induce  disease,  and  the  methods  of  coping  with  it. 

Considerable  research  has  been  carried  out  on  the 
diseases  of  truck  crops.  The  work  of  Professors  Stew- 
art, Selby,  Jones,  Orton,  Clinton,  Lutman,  Melhus, 
Manns,  Harter,  Sackett,  Whetzel,  and  of  others  has 
already  yielded  valuable  information  on  the  diseases 
and  their  control  in  the  case  of  some  of  our  staple 
food  crops.  Still,  in  the  case  of  many  diseases,  little 
is  known  as  yet  as  to  methods  of  treatment.  But 
much  is  to  be  looked  for  from  research  in  the  future. 


Introduction  xxix 

It  was  the  writer's  intention  to  avoid  technical 
terms  as  far  as  possible.  However,  it  was  found  ex- 
tremely difficult  to  omit  every  trace  of  a  technical 
vocabulary,  inasmuch  as  the  popular  terms  are  not 
always  adequate  in  identifying  a  disease  or  in  de- 
scribing its  causal  organism.  As  far  as  was  consistent 
all  popular  names  were  accepted  and  retained  in  this 
work.  However,  there  are  many  diseases  which 
have  as  yet  no  popular  names.  As  an  illustration 
may  be  mentioned  certain  spot  diseases  of  particular 
hosts.  These  spots  may  be  caused  by  different  fungi 
and  yet  resemble  each  other.  In  such  a  case  how  are 
we  to  name  these  diseases?  The  surest  way  to  avoid 
confusion  is  to  call  the  diseases  by  the  name  of  the 
causal  organism,  such  as  Phyllosticta  leaf  spot,  Cer- 
cospora  leaf  spot,  etc.  Professor  Stevens  has  sug- 
gested that  we  name  all  diseases  by  the  name  of  their 
causal  organism  and  add  to  it  the  term  "ose, "  such 
as  Phyllostictose,  Cercosporose,  Sclerotinose,  etc. 
The  writer  has  not  adopted  Stevens  terminology. 
In  many  cases  the  popular  name  of  a  disease  de- 
scribes it  far  better  than  a  technical  term  can  do.  To 
drop  altogether  such  valuable  popular  terminology 
would  only  confuse  the  practical  man.  For  instance, 
the  popular  term  for  lettuce  "drop"  is  far  more  sug- 
gestive than  "Sclerotinose." 

From  a  practical  consideration,  the  healthy  plant 
is  of  greater  importance  than  the  disease.  If  we  were 
to  bend  all  our  energy  and  skill  to  safeguarding  the 
health  of  our  crops,  we  would  not  be  pestered  with 
diseases.  This  is  the  point  of  view  of  this  work. 


xxx  Introduction 

For  this  reason,  too,  much  space  has  been  given  to  a 
consideration  of  the  healthy  hosts  and  of  the  soil,  the 
mother  of  all  vegetation. 

For  the  sake  of  convenience,  the  crops  here  con- 
sidered have  been  taken  up  in  the  natural  order  of 
families  to  which  they  belong.  The  families  have 
then  been  arranged  in  alphabetical  order,  and  the 
crops  in  each  family  taken  up  alphabetically  by  their 
popular  names.  On  the  other  hand,  the  diseases 
have  been  arranged  according  to  their  causes,  classi- 
fied according  to  the  system  generally  accepted  by 
students  in  mycology. 

The  present  work  is  intended  as  a  guide  to  the 
trucker  and  gardener,  and  to  the  student  in  Plant 
Pathology.  It  is  the  result  of  several  years  of  re- 
search in  truck  crop  diseases.  Where  information 
has  been  drawn  from  other  sources  full  references 
have  been  given,  so  far  as  possible  from  the  latest 
investigations.  The  writer  has  aimed  at  making 
this  work  as  br^ad  and  as  generally  useful  as  possible 
rather  than  confining  it  to  local  interest. 

Because  of  the  great  economic  importance  of  the 
subject  of  truck  crop  diseases,  it  is  felt  that  the  pres- 
ent work  fills  a  timely  want  and  needs  no  apology. 
We  cannot  expect  a  general  text -book  on  Plant  Path- 
ology to  go  into  lengthy  treatment  of  all  plant  dis- 
eases, and  even  less  so  with  those  of  the  trucking 
crops.  The  subject  in  itself  is  too  important  and  too 
broad  to  be  dealt  with  adequately  in  a  few  pages. 
The  time  will  undoubtedly  come  when  the  diseases 
of  every  important  crop  will  be  treated  separately  in 


Introduction  xxxi 

book  form.  The  Culture  and  Diseases  of  the  Sweet 
Pea,  by  the  writer,  was  an  attempt  in  that  direction. 
Meanwhile,  until  we  have  available  the  results  of 
more  extended  researches  on  particular  crops,  the 
present  work,  it  is  hoped,  will  fill  the  gap. 


PART  I 


CHAPTER  I 

THE  NORMAL  SOIL  AND  ITS   REQUIREMENTS 

THE  aim  of  this  chapter  is  to  study  the  conditions 
under  which  a  healthy  plant  lives  and  grows.  Such 
knowledge  will  prepare  us  to  consider  the  causes  or 
factors  which  are  responsible  for  abnormalities  and 
diseases.  Plants  are  endowed  with  life,  and  to  live 
they  must  have  food.  Part  of  the.  food  is  derived 
from  the  air,  but  they  cannot  subsist  on  air  alone. 
The  sustenance  of  plants  is  also  derived  from  the 
soil. 

It  is  to  be  regretted  that  laymen  often  regard  the 
soil  as  merely  a  conglomeration  of  inert  particles  of 
dead  rock.  If  this  were  true,  plant  life  would  be  an 
impossibility.  It  is  because  soils  are  teeming  with 
various  forms  of  organisms  beneficial  to  them  that 
plant  life  is  made  possible  therein.  The  science  of 
Soil  Bacteriology,  though  still  in  its  infancy,  has 
already  taught  us  much  to  help  make  the  trucking 
business  much  more  profitable  and  successful  than 
it  has  been  hitherto. 

Indeed  we  may  judge  a  soil  by  the  kind  of  flora 
which  predominates  there,  and  call  it  fertile  and 
healthy  when  this  germ  life  helps  to  make  it  a  f avor- 

3 


4  Diseases  of  Truck  Crops 

able  medium  for  the  plants.  On  the  contrary,  we 
call  it  sick  or  poor  when  it  teems  with  bacteria  and 
fungi  which  act  as  parasites  on  plants,  or  when  the 
beneficial  ones  are  absent  or  perform  their  duties 
imperfectly. 

STRUCTURE  AND  LIFE  HISTORY  OF  BACTERIA 

The  term  bacteria  (singular  bacterium),  or  microbe, 
or  germ,  refers  to  the  smallest  microscopical  form  of 
plant  life.  As  we  shall  see  later,  bacteria  are  but  one 
of  the  many  forms  of  life  in  the  soil.  The  first  man 
to  recognize  bacteria  was  Anton  van  Leeuwenhoek, 
a  native  of  Holland,  and  a  lens  maker  by  trade.  He 
made  use  of  the  microscope  in  testing  materials  for 
lens  making.  In  1675  he  happened  to  mount  in  a 
drop  of  water  some  tartar  which  he  scraped  off  from 
his  teeth.  To  his  great  surprise  he  discovered  mi- 
nute little  "animals"  which  moved  about  in  curious 
fashions.  In  1882,  Robert  Koch  succeeded  in  grow- 
ing bacteria  artificially  and  outside  their  natural 
environment.  Thus  was  laid  the  foundation  of  the 
modern  science  of  Bacteriology. 

Bacteria  are  very  simple  in  form.  We  recognize 
the  rod-shaped  known  as  Bacillus  (fig.  i  a),  the 
spherical  form  as  Coccus  (fig.  i  b),  and  the  corkscrew 
or  comma  form  as  Spirillum  (fig.  I  c).  Bacteria  are 
very  minute.  It  would  take  about  fifteen  to  twenty 
thousand  individual  bacteria  placed  end  to  end  to 
make  one  inch  in  length.  They  occur,  however,  in 
tremendous  numbers  and  this  enables  them  to  per- 


FIG.   i.     BACTERIA. 

a.   Rod  shaped,  b.  coccus,  c.  spirillum,  d.  plate  culture,  showing  bacterial  colonies 
isolated  from  soil. 


Normal  Soil  and  Its  Requirements      5 

form  wonderful  tasks,  as  we  shall  soon  see.  Bacteria 
multiply  in  the  simplest  ways.  A  single  individual 
upon  reaching  maturity  becomes  constricted  in  the 
center,  then  divides  in  two,  each  part  now  becoming 
a  separate  individual  capable  of  nutrition,  growth, 
and  multiplication.  It  has  been  estimated  by  scien- 
tists that  division  of  a  single  individual  takes  place 
about  every  twenty  minutes.  Granting  that  this 
rate  of  division  is  uninterrupted  for  twenty-four 
hours,  the  descendants  of  one  germ  would  be  in  round 
numbers  1,800,999  trillions.  These  when  placed 
end  to  end  would  make  a  string  two  trillion  miles 
long,  or  a  thread  long  enough  to  go  around  the  earth 
at  the  equator  seventy  million  times.  It  would  take 
a  ray  of  light  four  months,  traveling  as  it  does,  to 
pass  from  one  end  of  it  to  another. 

Individual  bacteria  can  be  detected  only  with  a 
compound  microscope.  When  grown  on  artificial 
media  and  under  aseptic  conditions,  all  the  descend- 
ants of  a  single  parent  cell  live  together  and  constitute 
a  colony,  which  becomes  visible  to  the  naked  eye  as 
a  creamy  jellylike  drop  (fig.  I  d). 

* 

RELATIONSHIP  OF  BACTERIA  TO  THE  FUNCTION  OF 
A  SOIL 

The  health  of  a  soil  as  shown  in  its  fertility  is  in- 
timately connected  with  the  kind  of  bacteria  present 
in  it.  We  are  as  yet  in  the  dark  as  to  the  possible 
function  of  numerous  groups  of  the  soil  organisms. 
Bacteriologists  are  seeking  to  discover  their  proper 


6  Diseases  of  Truck  Crops 

functions.  A  recent  exhaustive  study x  of  Actinomy- 
ces,  or  thread  bacteria,  in  the  soil  seems  to  show  that 
they  serve  to  decompose  grass  roots,  being  more 
numerous  in  sod  than  in  cultivated  land.  Other 
groups  of  bacteria  undoubtedly  must  perform  other 
important  functions. 

The  mere  presence  of  friendly  bacteria  in  the  soil, 
however,  would  be  insufficient  to  assure  the  welfare 
of  our  cultivated  lands.  What  concerns  us  most  is 
the  work  that  they  perform.  Most  of  the  plant's 
food  as  it  is  found  in  the  soil  is  in  a  crude  and  una- 
vailable form.  The  bits  of  mineral  matter,  the 
manure  or  fertilizer,  in  the  truck  patches  all  con- 
tain plant  foods  but  in  a  form  which  plants  cannot 
readily  use;  they  must  be  softened  and  predigested 
and  this  work  is  done  by  the  friendly  organisms. 
Plant  food  is  therefore  directly  dependent  on  the 
work  of  these  minute,  scavengers.  An  intimate  re- 
lation exists  between  the  higher  and  the  lower  forms 
of  plant  life,  the  one  depending  on  the  other. 

DISTRIBUTION  OF  SOIL  BACTERIA 

For  a  practical  purpose  we  ought  to  know  in  what 
soil  and  at  what  depth  the  beneficial  bacteria  are 
most  likely  to  abound.  Since  the  presence  of  bac- 
teria is  necessary  to  maintain  the  fertility  of  a  normal 
healthy  soil,  it  is  essential  to  study  the  main  factors 
that  determine  their  increase  or  decrease.  We  can- 
not expect  to  find  them  equally  distributed  in  differ- 

1  Conn,  Joel  H.,  New  York  (Geneva)  Agr.  Expt.  Sta.  Bui.  52  : 
3-1 1,  1916. 


Normal  Soil  and  Its  Requirements      7 


ent  depths  of  the  same  soil.  Brown1  has  shown  that 
bacteria  are  generally  more  abundant  in  the  upper 
eight  inches.  Table  I ,  adapted  from  Brown  throws 
much  light  on  this  phase  of  the  problem. 

TABLE  i 

Bacteria  as  Found  in  Various  Depths  of  Soil  and  Under 
Different  Cropping  Systems       - 


Plot 
No.' 

Lab. 
No. 

Depth  of 
Sampling 

Bacteria  per  Gram  of  Air-Dry  Soil 

I 

II 

III 

IV 

Average 

601 

A 

4  in. 

2033000 

1627000 

1793000 

1555000 

1752000 

B 

8  in. 

1437000 

I2IIOOO 

I24IOOO 

1104000 

1248250 

C 

12  in. 

541000 

567000 

559000 

525000 

546000 

D 

i6in. 

287000 

292OOO 

3I2OOO 

302000 

298250 

E 

20  in. 

147000 

154000 

159000 

154000 

153500 

F 

24  in. 

92300 

96500 

95100 

91500 

93850 

G 

30  in. 

49900 

46300 

50900 

46900 

48500 

H 

36  in. 

32900 

30000 

33100 

30400 

31600 

602 

A 

4  in. 

3102000 

287OOOO 

29I7OOO 

2947000 

2959000 

B 

8  in. 

2238000 

2I77OOO 

2105000 

2258000 

2194500 

(J 

12  in. 

498000 

531000 

531000 

528000 

522000 

D 

i6in. 

255000 

328000 

316000 

314000 

304250 

E 

20  in. 

182000 

I92OOO 

188000 

177000 

184750 

F 

24  in. 

89200 

93300 

91600 

88300 

90600 

G 

30  in. 

53300 

54900 

53100 

51800 

54275 

H 

36  in. 

31700 

35700 

34200 

31300 

33225 

604 

A 

4  in. 

4606000 

3908000 

42IOOOO 

3932000 

4164000 

B 

8  in. 

3132000 

2834OOO 

2976OOO 

2793000 

2943750 

C 

12  in. 

1016000 

882OOO 

901000 

831000 

907500 

D 

i6in. 

320000 

309000 

3IIOOO 

320000 

315000 

E 

20  in. 

155000 

163000 

156000 

149000 

155750 

F 

24  in. 

89400 

96100 

92900 

88900 

91825 

G 

30  in. 

51900 

55800 

55000 

52400 

53775 

H 

36  in. 

35ioo 

36600 

34900 

32600 

34800 

1  Brown,P.  E.,  Iowa  Agr.  Expt.Sta. Research  Bui. 8 : 283-321, 1912. 
3  Plot  No.  601. — Continuous  corn.    602. — 2-year  rotation,  corn 
and  oats.     604. — 3-year  rotation,  corn,  oats,  and  clover. 


8  Diseases  of  Truck  Crops 

In  studying  Table  I  we  find  that  in  every  case 
there  is  a  marked  decrease  in  soil  organisms  with  each 
increase  in  the  depth  of  the  soil  tested.  It  was  fur- 
ther found  by  Brown  that  the  moisture  content  was 
higher  for  four  inches  than  for  a  greater  depth.  It 
seems  evident  that  the  decrease  of  soil  bacteria  below 
twelve  inches  is  dependent  not  so  much  on  moisture 
but  rather  on  a  decrease  of  air  in  the  lower  substratum. 
It  must  not  be  expected  that  the  data  given  in  Table 
I  are  applicable  to  every  locality.  Differences  in 
the  mechanical  and  chemical  composition  of  the  soil 
and  subsoil,  differences  in  topography,  climate,  and 
weather  conditions,  will  all  no  doubt  tend  to  influence 
more  or  less  the  increase  or  decrease  of  bacteria. 

INFLUENCE  OF  DEPTH  OF  CULTIVATION  ON  THE 
NUMBER  OF  SOIL  BACTERIA 

The  work  of  King  and  Doryland1  has  shown  that 
the  depth  of  cultivation  is  a  potent  factor  in  influ- 
encing the  number  of  bacteria  in  the  soil.  This  is 
briefly  summarized  by  them  in  Table  2. 

TABLE  2 
Influence  of  Depth  of  Cultivation  on  Soil  Bacteria 

Silt- 
plowed  4  inches  deep  increases  the  number  of  bacteria. .  1546% 
plowed  6  inches  deep  increases  the  number  of  bacteria. .  10.94% 
plowed  8  inches  deep  increases  the  number  of  bacteria.  .24.20% 
plowed  10  inches  deep  increases  the  number  of  bacteria . .  26.89% 

1  King,  W.  E.,  and  Doryland,  Ch.,  Kansas  Agr.  Expt.  Sta.  Bui. 
161  1211-242,  1909. 


Normal  Soil  and  Its  Requirements      9 

Sand- 
plowed  4  inches  deep  increases  the  number  of  bacteria.  .35.06% 
plowed  6  inches  deep  increases  the  number  of  bacteria. .  13.53% 
.  plowed  8  inches  deep  increases  the  number  of  bacteria .  .22.90% 
plowed  i o  inches  deep  increases  the  number  of  bacteria . .  5.1 1  % 

THE  INFLUENCE  OF  MANURE  ON  THE  NUMBER  OF 
SOIL  BACTERIA 

Besides  cultivation,  there  are  other  treatments 
which  may  lead  to  an  increased  bacterial  flora  in  the 
soil.  As  shown  by  Temple1  such  a  result  is  obtained 
through  the  application  of  manure.  In  working  with 
a  newly  cleared  sandy  loam,  and  applying  fresh  cow 
manure  (this  included  solid  excreta  and  no  bedding), 
at  the  rate  of  ten  tons  per  acre,  Temple  obtained  the 
following  results  as  shown  in  Table  3. 

TABLE  3 
Showing  Number  of  Bacteria  per  Gram  of  Dry  Soil 


Soil  No.  326 

Soil  No.  3260, 

Date 
March  26,  1909  

No  Manure 
1,220,000 

With  Manure 
1,220,000 

April  i,  1909  

1.633  ooo 

4..3OO.OOO 

April  Q,  IQOQ  . 

6,120,000 

I4,OOO,OOO 

April  15,  IQOQ.. 

3.780.000 

IO,6lO,OOO 

April  22,  1909  

2.730.000 

5,860  ooo 

April  29,  1909  ...    . 

2.  77O.OOO 

3,34.0.000 

May  6,  1909  

s.sio.ooo 

5,190,000 

As  further  evidence  that  manure  increases  the  soil 
flora,  Temple  used  a  clay  loam,  dividing  it  in  the 
following  manner;  and  treated  as  follows: 

1  Temple,  J.  C.,  Georgia  Agr.  Expt.  Sta.  Bui.  95  : 6-35,  1911. 


10 


Diseases  of  Truck  Crops 


Plat  No.  i — Stable  manure. 

Plat  No.  4 — Sodium  nitrate. 

Plat  No.  5— A  complete  fertilizer,  PKN. 

Plat  No.  6— Nothing,  check. 

The  effect  of  these  treatments  is  briefly  summarized 
in  Table  4. 

TABLE  4 
Colonies  per  Gram  of  Dry  Soil 


Date 

Plat  No.  i 

Plat  No.  4 

Plat  No.  5 

Plat  No.  6 

Dec.  9,  1910  
March  30,  1911  
May  26,  1911  

28,230,000 
18,500,000 
20,200,000 

11,430,000 
9,150,000 
4,850,000 

19,850,000 
8,040,000 
6,720,000 

8,250,000 
6,240,000 
5,010,000 

The  above  Table  shows  that  although  sodium  ni- 
trate or  a  complete  fertilizer  increases  the  soil 
flora,  neither  one  can  be  compared  to  manure  in 
efficiency. 

STRUCTURE  AND  LIFE  HISTORY  OF  FUNGI 

Besides  bacteria  of  all  sorts,  our  cultivated  soils 
are  also  teeming  with  fungi.  The  true  function  of 
the  latter  remains  to  be  studied.  There  seems  no 
doubt,  however,  that  certain  fungi  like  certain  bac- 
teria in  the  soil  work  on  the  organic  and  the  mineral 
matter  to  make  it  available  as  plant  food.  Parasitic 
fungi  depend  for  their  food  on  living  plants  alto- 
gether. Examples  of  these  are  the  Uredinales,  the 


FIG.  2.     STRUCTURE  OF  FUNGI. 


a  Fruiting  branch  of  Penicillium,  showing 
conidiophores  and  conidia,  b.  mycelium 
of  Penicillium,  c.  an  individual  conidiopnore 
and  chain  of  conidia  of  Penicillium,  d.  two 
conidia  of  Penicillium,  showing  attachment 
of  spores  in  the  chain,  e.  fertilization  ot 
female  oogonium  by  male  anthendium,  /. 
mature  oospore,  g.  fruiting  stalks  of  Rn}zo- 
pus,  h,  individual  fruiting  head  of  Rhizo- 
pus  showing  spores,  *.  sexual  fertilization 
and  k.  zygospore  of  Rhizopus  showing  spores, 
/.  perithecium,  showing  asci  and  ascospores, 
or  winter  spores,  m.  Pycnidium  or  sac  in 
which  the  summer  spores  are  borne. 


Normal  Soil  and  Its  Requirements    11 

cause  of  the  true  rust  diseases.  Saprophytic  fungi 
are  those  which  depend  for  their  food  on  the  dead  and 
decaying  organic  matter  in  the  soil.  Between  these 
two  extremes  there  are  intermediaries.  As  an  illus- 
tration of  a  soil  fungus  may  be  taken  the  ordinary 
blue  mold,  Penicillium  expansum  Lk.  This  organ- 
ism is  made  up  of  colorless  feeding  threads  techni- 
cally known  as  hypha?  or  mycelium  (fig.  2  b).  The 
spores,  which  correspond  to  the  seed  of  higher  plants, 
are  borne  on  short  stalks  which  bear  broomlike  tufts 
composed  of  chains  of  small  bluish,  round  bodies,  the 
spores  (fig.  2  a-c). 

Fungi  differ  from  the  higher  plants  in  their  nu- 
trition and  mode  of  reproduction.  Fungi  have  no 
green  coloring  matter,  chlorophyll,  and  are  thus 
unable  to  manufacture  their  own  carbon  by  the  de- 
composition of  carbon  dioxide  as  do  green  plants. 
This  is  why  fungi  must  depend  for  their  supply  of 
carbon  on  dead  organic  matter  or  on  the  higher  plants. 
Unlike  the  green  plants,  fungi  have  no  flowers  and 
reproduce  by  means  of  spores  (fig.  2  g-h).  It  has 
been  estimated  that  over  61,000  species  of  fungi 
have  been  found  and  described  on  the  higher  plants. 
The  Soil  Bacteriologist  however  has  scarcely  touched 
on  the  soil  fungi. 

Fungi  are  classified  according  to  the  mode  of  spore 
formation.  In  some  the  spores  are  formed  by  a 
regular  sexual  union  of  a  female  egg  known  as  oogon- 
ium  and  of  a  male  element,  the  antheridium  (fig.  2  e, 
i,  k).  The  resultant  fertilized  spore  egg  is  known  as 
oospore  (fig.  2  f).  The  latter  germinates  by  sending 


12  Diseases  of  Truck  Crops 

out  a  germ  tube,  or  as  is  more  generally  the  case,  by 
the  outer  wall  dissolving  and  the  inner  mass  breaking 
up  into  small  bits  of  naked  protoplasm  known  as 
zoospores.  Most  fungi  have  two  spore  stages,  the 
summer  form  intended  for  rapid  dissemination  and 
spread,  the  winter  form  intended  to  carry  it  over 
through  cold  or  any  other  unfavorable  weather  con- 
ditions. The  term  conidia  is  applied  to  all  spore 
forms  borne  free  on  special  fruiting  stalks  known 
as  conidiophores  (fig.  2  a).  A  pycnidium  is  a  sac- 
like  body  (fig.  2  m)  in  which  are  borne  the  summer 
spores.  A  perithecium  is  a  sac-like  body  (fig.  2  1) 
which  bears  the  winter  spores  of  certain  fungi. 
Other  terms  here  used  in  describing  parts  of  fungi 
will  be  found  in  the  glossary. 

NATURE  AND  FUNCTION  OF  A  HEALTHY  SOIL  FLORA 

The  function  of  a  normal  soil  is  to  provide  avail- 
able plant  food.  About  95  per  cent,  of  the  com- 
bustible weight  of  a  growing  plant  is  made  up  of 
carbon,  hydrogen,  and  oxygen  and  nitrogen.  The 
remaining  5  per  cent,  constitutes  the  mineral  or  the 
ash  of  the  plant.  Carbon,  hydrogen,  and  oxygen  are 
taken  in  the  form  of  carbonic  acid  and  water ;  nitrogen 
from  nitrates  produced  by  bacteria  out  of  organic 
matter  of  the  soil.  The  ash  or  the  mineral  elements 
of  the  plant  are  taken  directly  from  the  soil.  Neither 
the  organic  nor  the  mineral  elements  are  in  a  form 
which  plants  can  make  use  of  until  they  have  been 
acted  on  by  certain  definite  organisms  in  the  soil. 


Normal  Soil  and  Its  Requirements    13 

A.    THE  TRANSFORMATION  OF  CARBON 

Cellulose,  which  is  but  a  form  of  carbon,  consti- 
tutes a  large  per  cent,  of  the  woody  tissue  of  plants. 
Soils  contain  large  amounts  of  cellulose  and  this  un- 
doubtedly helps  to  maintain  their  proper  physical  con- 
dition. Straw  manure,  or  green  vegetable  matter  all 
contain  large  amounts  of  cellulose.  When  it  is  in- 
corporated in  the  soil,  living  plants  cannot  make  use 
of  it,  because  of  its  complex  form.  It  therefore  must 
first  undergo  a  certain  decomposition.  This  is  ac- 
complished by  a  group  of  soil  bacteria  known  as 
Amylobacter.  These  feed  on  the  dead  vegetable 
cellulose,  breaking  it  up  and  reducing  it  back  to  car- 
bon dioxide,  hydrogen,  and  fatty  acids.  The  carbon 
dioxide  either  returns  to  the  air  to  replenish  the  at- 
mospheric supply,  or  unites  with  water  to  form  car- 
bonic acid  and  soil  carbonates.  The  carbon  dioxide 
is  taken  in  by  the  plants  either  directly  from  the  air 
through  the  leaves,  or  from  the  soil  in  some  carbon- 
ate form.  Thus  we  see  that  it  is  not  the  cellulose  nor 
the  product  of  its  decomposition  that  furnishes  plant 
food,  but  certain  inorganic  elements  which  are  set  free 
in  its  decomposition. 

B.    ELABORATION  OF  AVAILABLE  NITROGEN 

From  the  viewpoint  of  plant  nutrition,  nitrogen 
is  unquestionably  the  most  important  of  all  elements. 
The  nitrogen  of  the  air,  although  totalling  about  79 
per  cent,  of  it,  is  not  in  an  available  form.  In  the 
transformation  of  proteids  into  available  nitrogen 


14  Diseases  of  Truck  Crops 

in  the    soil  two  definite  processes  take  place,  all 
thanks  to  the  work  of  certain  soil  bacteria. 

1.  AMMONIFICATION.     In  this  process,   the  soil 
bacteria  attack  the  complex  proteids  and  convert 
them  into  ammonia.     The  odor  of   ammonia  from 
decomposed   urea,  manure,    or   any  other   organic 
matter  is  always  an  indication  that  ammonification 
takes  place.     According  to  Sackett1  and  others  the 
ability  to  bring  about  this  change  is  attributed  to  the 
following  soil   bacteria:  Bacillus  mycoides.  Bacillus 
proteus  vulgaris,  Bacillus  mesentericus  vulgatus,  Bacil- 
lus subtilis,  Bacillus  janthinus,  Bacillus  coli-communis, 
Bacillus  megatherium,  Bacillus  fluorescens  liquefaciens, 
Bacillus  fluorescens  putridus,  and  Sarcina  lutea. 

2.  NITRIFICATION.     Both  ammonia  and  ammonia 
compounds  are  forms  of  nitrogen  that  are  not  yet 
readily  available  to  plants.     They  must  be  changed 
further  into  simpler  compounds  or,  as  the  process  is 
known,  must  undergo  nitrification.     The  ammonia 
is  first  oxidized  into  nitrous  acid  and  nitrates.      This 
is   accomplished   by   two   species   of   soil   bacteria, 
Nitrosomonas  and  Nitrosococcus.     The  nitrates  are 
then  oxidized  into  nitric  acid  and  nitrates,  through 
the  work  of  the  bacterium  Nitrobacter.     The  nitrates 
are  the  only  forms  of  nitrogen  which  plants  can  use. 

C.  ACTION  OF  SOIL  FLORA  ON  MINERAL  SUBSTANCES 

We  have  already  pointed  out  that  the  inert  mineral 
substances  in  the  soil  are  not  in  a  form  in  which 

«  Sackett,  W,  G.,  Colorado  Agr.  Expt.  Sta.  Bui.  196  : 3-39,  1916. 


Normal  Soil  and  Its  Requirements    15 

plants  can  readily  assimilate  them.     These  too  must 
first  be  acted  upon  by  certain  soil  bacteria. 

1.  CHANGES    OF    PHOSPHATES.    Phosphates    as 
they  commonly  occur  in  nature  are  but  little  soluble 
in  water.     This  is  why  they  cannot  be  used  in  their 
first  form,  although  they  are  required  by  most  plants. 
Soils  deficient  in  this  element  may  be  improved  by 
such  fertilizers  as  superphosphate  of  lime,  ground 
bone,  phosphate  rock,  or  Thomas  slag.     In  the  pro- 
cess of  decomposition  that  organic  matter  must  un- 
dergo as  it  becomes  available  for  plant  food,  large 
quantities   of   carbon   dioxide   are   liberated   which 
unite  with  the  water  in  the  soil  to  form  carbonic  acid. 
This  acid  attacks  the  insoluble  phosphates,  trans- 
forms them  into  superphosphates, — the  only  form 
soluble  in  water, — and  renders   them  available  to 
plant  life. 

2.  CHANGES  IN  POTASSIUM,  SULPHUR,  AND  IRON. 
Like  phosphorus,  potassium,  sulphur,  and  iron  are 
made  available  for  plants  through  the  indirect  action 
of   soil   bacteria.     The   carbon    dioxide   and   other 
organic  acids  produced   during  the  fermentation  of 
organic  matter,   attack  the  potash  feldspar  which 
occurs  in  the  soil.     The  product  is  potassium  car- 
bonate which  is  soluble  in  water  and  hence  readily 
taken  up  by  plants.     The  nitric  acid  which  is  formed 
during  nitrification  may  also  combine  with  the  raw 
potash  in  the  soil  forming  potassium  nitrate  which  is 
a  form  available  for  plants. 

As  a  result  of  the  activity  of  soil  bacteria,  hydrogen 
sulphide  is  evolved  from  the  decomposition  of  pro- 


1 6  Diseases  of  Truck  Crops 

teids.  The  sulphur  may  be  further  changed  into 
sulphur  dioxide,  and,  when  combining  with  water  and 
oxygen,  into  free  sulphuric  acid.  The  latter  read- 
ily combines  with  calcium  or  magnesium,  forming 
calcium  or  magnesium  sulphate.  The  plant  obtains 
sulphur  for  the  construction  of  its  proteids  from  some 
of  the  soluble  sulphates. 

How  TO  MAINTAIN  THE  FERTILITY  OF  SOILS 

We  have  already  seen  that  the  fertility  of  a  soil  is 
directly  dependent  upon  the  activity  of  certain  bene- 
ficial bacteria.  The  latter  constitute  the  life  of  a  soil. 
It  is  therefore  evident  that  for  a  soil  to  produce  its 
maximum,  its  germ  flora  must  receive  careful  con- 
sideration at  the  hands  of  truckers  and  gardeners. 
We  must  at  any  cost  encourage  these  organisms  to 
do  their  full  duty  at  all  times.  Should  they  cease 
activity  the  soil  would  become  barren. 

There  is  no  doubt  that  plants  remove  large  quan- 
tities of  plant  food  from  the  soil.  Headen1  has  cal- 
culated that  for  80,000  tons  of  sugar  beet,  there  are 
consumed  as  fertilizers,  331  tons  of  potash,  worth 
$31,100;  71  tons  of  phosphoric  acid  worth  $5,680; 
1 60  tons  of  nitrogen  worth  $54,400,  making  a  total 
of  $91,180,  or  a  trifle  over  one  dollar  per  ton.  What 
is  true  for  the  sugar  beet  is  true  for  every  other 
trucking  crop.  In  other  words,  soil  fertility  is  capa- 
ble of  being  exhausted.  Most  of  it  may  be  returned 
in  the  form  of  manure  and  chemical  fertilizers,  but 

1  Headen,  W.  P.,  Colorado  Agr.  Expt.  Sta.  Bui.  99: 3-16,  1905. 


Normal  Soil  and  Its  Requirements    17 

these  are  very  expensive  and  reduce  the  net  profit 
from  the  crops.  The  object  of  every  intelligent 
trucker  should  therefore  be  to  reduce  his  manure  and 
fertilizer  bills  by  encouraging  his  soil  bacteria  to  man- 
ufacture the  greatest  amount  of  the  available  food 
which  his  crops  require.  Like  any  other  living  form 
these  bacteria  require  certain  conditions  of  life  if  they 
are  to  thrive. 

MAINTAINING  THE  NITROGEN  SUPPLY 

The  nitrifying  bacteria  are  air-loving  organisms. 
Hence  the  more  aeration  we  give  them,  the  more  pro- 
nounced their  activity.  Schlosing1  determined  that 
when  a  soil  was  entirely  void  of  oxygen  the  nitrates 
were  reduced,  and  brought  about  an  actual  evolution 
of  free  nitrogen  which  is  useless  to  the  plant.  With 
1.5  per  cent,  of  oxygen  nitrification  was  marked. 
When  6  per  cent,  oxygen  was  added  to  the  soil  nitri- 
fication was  more  than  doubled.  It  is  therefore 
evident  that  cultivation  which  aims  at  soil  aeration 
also  accelerates  nitrification.  The  effect  of  soil 
aeration  cannot  be  too  strongly  emphasized.  Ac- 
cording to  Chester,2  every  cultivation  of  the  soil 
with  its  attendant  aeration  is  equivalent  to  a  dressing 
of  nitrate  of  soda  in  its  cheapest  form.  If  we  realized 
this,  and  that  nitrate  fertilizers  are  usually  the  most 
costly,  the  alert  trucker  would  learn  the  economy  of 
more  cultivating. 

1  Schlosing,  Compt.  Rend.  Acad.  Sci.  Paris,  Ixxvii,  203-253. 
»  Chester,  F.  D.,  Pa.  State  Dept.  of  Agr.  Bid.  98:  9-88,  1912. 


1 8  Diseases  of  Truck  Crops 

Besides  oxygen,  the  nitrifying  organisms  demand, 
as  an  indispensable  condition  for  work,  a  sufficient 
moisture  in  the  soil.  In  dry  soils  and  during  dry 
weather,  nitrification  is  almost  suspended  within  the 
upper  layers  of  soil.  A  third  important  factor  is  the 
chemical  reaction  of  the  soil.  The  nitrifying  organ- 
isms work  best  when  the  soil  gives  a  slight  alkaline 
reaction.  Too  much  alkalinity,  however,  like  too 
much  acidity,  is  detrimental  as  we  shall  see  further  on. 
Nitrification  is  further  dependent  on  soil  temperature. 
At  99  degrees  Fahrenheit  it  is  at  its  highest.  A  de- 
gree less  than  54  F.  retards  it  considerably.  At  122 
degrees  F.  very  little  nitrate  is  produced,  and  at  131 
degrees  F.  nitrification  ceases  entirely.  The  physical 
condition  of  the  soil  is  another  important  element  to 
be  considered.  The  highest  rate  of  nitrification  is 
found  in  truck  lands,  that  is,  in  the  sandy  loams. 

NITROGEN  FIXATION  FROM  THE  AIR 

It  has  been  the  common  knowledge  of  farmers  and 
truckers  that  legume  plants,  such  as  peas  and  beans, 
cause  the  soil  on  which  they  are  grown  to  become 
more  productive.  It  is  not  necessary  here  to  enter 
into  an  abstract  discussion  of  this  phenomenon. 
Suffice  it  to  say,  that  science  has  definitely  shown 
that  there  is  a  bacterial  soil  organism,  Pseudomonas 
radicicola,  which  is  capable  of  fixing  the  free  nitro- 
gen from  the  air.  This  organism  attacks  the  young 
rootlets  of  the  legume  crops  as  other  parasitic  forms 
also  do.  Its  presence  in  the  root  results  in  a  nodule 


Normal  Soil  and  Its  Requirements    19 

or  swelling.  Soon,  however,  it  loses  its  parasitic 
character  and  becomes  an  agent  for  fixing  the  free 
nitrogen  of  the  air,  which  is  then  stored  up  in  the 
root  nodule.  In  this  form  the  nitrogen  is  consumed 
by  the  plant  itself.  As  far  as  is  known,  P.  radicicola 
can  thrive  on  the  roots  of  legume  plants  only.  The 
Rhode  Island  Experiment  Station1  has  found  that 
an  acre  of  soy  beans  for  instance  may  fix  about 
I  OCX)  pounds  of  nitrogen  from  the  air  during  a  period 
of  five  years,  or  200  pounds  per  year.  One  hundred 
and  forty  pounds  of  the  200  were  removed  with  the 
crop,  and  60  pounds  remained  in  the  field.  Since 
one  pound  of  nitrogen  was  worth  at  least  i6c.,  200 
pounds  would  cost  $32.  We  must  not,  of  course, 
suppose  that  every  acre  of  soy  beans  would  produce 
200  pounds  of  nitrogen  every  year.  This  would 
depend  somewhat  on  the  nature  of  the  soil,  the  degree 
of  moisture,  the  amount  of  oxygen,  and  other  condi- 
tions congenial  or  unfavorable.  What  is  certain, 
however,  is  that  every  alert  gardener  and  trucker 
should  learn  to  use  legumes  more  extensively  in  his 
system  of  cropping. 

Soils  which  have  grown  leguminous  crops  for  a 
period  of  years  are  well  supplied  with  P.  radicicola. 
Other  soils  are  deficient  in  it  and  must  be  artificially 
inoculated.  The  numerous  types  of  pure  cultures 
of  the  organism  sold  in  liquid  form  have  as  a  rule 
proven  a  failure.  The  organism  dies  out  or  loses  its 
effectiveness  in  the  artificial  liquid  media.  The  best 
forms  of  pure  cultures  now  used  are  those  grown  on 

1  Rhode  Island  Agr.  Expt.  Sta.  Bui.  147. 


20  Diseases  of  Truck  Crops 

sterilized  soil.  This  method  has  been  developed  at 
Cornell  University.  The  soil  is  after  all  the  natural 
and  best  medium  where  soil  bacteria  can  grow.  On 
it  P.  radicicola  lives  longer,  and  hence  when  it  is  used 
for  inoculation,  better  success  may  be  expected. 
The  Alphano  Humus  Co.  of  New  York  City  have  on 
the  market  cans  with  sterilized  soils,  in  which  the 
legume  bacteria  have  been  introduced.  Each  can  is 
sufficient  to  inoculate  one  acre  of  soil.  The  ability  of 
the  organism  of  one  legume  crop  to  inoculate  another 
crop  has  long  been  a  subject  of  discussion  and  has  not 
as  yet  been  satisfactorily  answered.  Garman  and 
Didlake1  have  shown  that  there  exist  six  different 
species  of  legume  organisms.  For  example  they 
found  that  the  organism  of  alfalfa  is  the  same  as  or 
similar  to  the  one  which  works  on  the  sweet  clover 
(Melilotus  alba),  trefoil  or  black  medick  (Melilotus 
lupulina),  and  bur  clover  (Melilotus  denticulata) . 
This  same  organism,  however,  cannot  produce  nod- 
ules on  the  roots  of  any  species  of  Trifolium,  of  Vicia, 
Pisum,  Vigna,  Glycine,  or  Phaseolus.  The  organisms 
of  all  the  species  of  Trifolium  (clover)  are  one  and  the 
same.  The  organisms  of  all  the  species  of  the  vetch 
and  garden  pea  are  one  and  the  same.  They  cannot 
work,  however,  on  red  or  crimson  clover,  or  on  alfalfa. 
The  cowpea  organism  seems  to  be  adapted  to  the 
cowpea  only.  The  same  thing  appears  to  be  true  for 
the  soy  bean  organism  and  for  that  of  the  garden 
bean.  Therefore  when  a  land  is  to  be  inoculated 

1  Garman,  H.  and  Didlake,  Mary,  Kentucky  Agr.  Expt.  Sta.  Bui. 
184:  343-363,  I9H. 


Normal  Soil  and  Its  Requirements    21 

with  the  garden  bean  organism,  for  instance,  none 
must  be  used  but  those  taken  from  the  bean.  Under 
ordinary  conditions,  where  a  soil  is  known  to  produce 
healthy  crops  of  one  (legume)  variety,  some  of  that 
soil  may  be  used  to  inoculate  other  soils  intended  for 
the  same  crop. 

ECONOMICAL  USE  OF  COMMERCIAL  FERTILIZER 

A  knowledge  of  the  functions  of  soil  bacteria  and 
a  proper  management  of  the  soil  means  a  saving  of 
commercial  fertilizer  and  the  proper  maintenance  of 
soil  fertility.  In  trucking  more  than  in  any  other 
phase  of  farming,  the  soil  is  being  made  to  produce 
the  whole  year  around.  This  is  especially  true  for 
our  Southern  States  where  the  summer  and  fall 
seasons  are  longest,  or  where  the  winters  are  very 
mild.  It,  therefore,  often  becomes  necessary  to  use 
chemical  fertilizers  to  supplement  the  work  of  the 
soil  bacteria.  This  is  especially  true  for  some  par- 
ticular crops  which  draw  heavily  on  certain  mineral 
constituents.  In  order  to  obtain  the  greatest  re- 
sults from  the  use  of  chemical  fertilizers,  the  follow- 
ing items  should  be  carefully  considered. 

1.  THE  LOCATION  OF  THE  FIELD.     Uplands  or 
hillsides  will  require  heavier  application  of  fertilizer 
since  some  of  it  is  likely  to  be  carried  off  by  washing. 
Lowlands,  especially  those  near  uplands  which  wash 
badly,  generally  require  less. 

2.  THE  CHARACTER  OF  THE  SOIL.     The  chemical 
composition  of  the  soil  has  a  marked  influence  on  the 


22  Diseases  of  Truck  Crops 

effect  of  fertilizers.  A  chemical  analysis  of  the  soil 
will  enable  the  trucker  to  make  a  more  economical 
use  of  his  fertilizer.  If  a  land,  for  instance,  contains 
too  much  iron  and  aluminium,  applied  phosphate 
fertilizers  may  be  modified  into  ferric  and  aluminium 
phosphate,  which  become  slowly  available  to  plants. 
On  the  other  hand  when  phosphate  fertilizers  are 
changed  in  the  soil  into  tricalcium  phosphate  it 
becomes  available  more  readily.  Sandy  soils  are 
generally  quick  to  respond  to  fertilization;  they  can 
therefore  stand  heavier  application  than  the  cold  clay 
soils  which  respond  more  slowly.  In  the  latter,  the 
fertilizers  are  likely  to  be  converted  into  forms  un- 
available to  plants.  The  trucker  should  therefore 
avoid  depending  altogether  on  the  use  of  chemical 
fertilizers.  The  best  results  are  always  obtained  and 
the  fertility  of  the  soil  best  preserved  when  the  use  of 
chemical  fertilizer  is  supplemented  with  animal  or 
green  manures. 


CHAPTER  II 

SICK   SOILS   NOT   INFLUENCED    BY    PARASITES 

WE  have  seen  that  a  normal  and  healthy  soil  is 
one  in  which  the  beneficial  soil  flora  is  at  its  maximum 
of  normal  activity,  making  the  food  of  the  plant 
assimilable.  We  have  to  discuss  the  abnormal  or 
sick  soils  now.  In  this  class  we  include  those  which 
are  either  physically  or  chemically  so  constituted  as 
to  have  a  detrimental  effect  on  the  activity  of  the 
soil  flora;  and  those  which  are  overrun  with  organ- 
isms directly  parasitic  on  the  plants  grown  in  that 
soil.  There  are  five  classes  to  be  considered  in  the 
first  division. 

I.    DENITRIFIED  SOILS 

This  detrimental  condition  in  the  soil  is  brought 
about  by  a  group  of  undesirable  organisms,  some 
of  which  are  Bacillus  ramosus,  B.  pestifer,  B. 
mycoides,  B.  subtilis,  B.  mesentericus  vulgatus. 
In  Chapter  I  we  have  seen  that  the  nitrifying 
bacteria  oxidize  the  nitrogen  and  make  it  avail- 
able for  plants.  In  denitrification,  the  harmful 
bacteria  tend  to  reconvert  the  available  nitrogen 
into  a  non-available  form,  or  else  to  liberate  it  into 
the  air,  where  it  may  be  considered  as  lost  so 

23 


24  Diseases  of  Truck  Crops 

far  as  the  crops  are  concerned.  Most  trucking 
lands  contain  the  nitrifying  and  denitrifying  organ- 
isms in  about  equal  proportions.  To  encourage 
the  activity  of  the  one  over  the  other  is  the  aim 
of  intelligent  trucking.  The  denitrifying  bacteria 
thrive  best  in  an  abundance  of  carbohydrate  foods. 
Fresh  coarse  manure  with  a  high  percentage  of  straw, 
when  applied  to  the  soil,  will  favor  denitrification. 
It  should  therefore  be  avoided  as  far  as  is  possible. 
There  are,  however,  market  gardeners  who  often  use 
as  much  as  fifty  tons  of  such  manure  per  acre  in  ad- 
dition to  a  nitrate  fertilizer.  Such  action  is  very  likely 
to  encourage  denitrification  because  of  the  large 
amount  of  carbohydrates  incorporated  in  the  soil. 

Indirectly  denitrification  will  finally  cause  various 
physiological  plant  troubles,  most  of  which  are  little 
understood.  Poor  growth  and  the  shedding  of 
blossoms  will  characterize  plants  deprived  of  avail- 
able nitrogen  food.  Denitrification  may  largely  be 
prevented.  A  judicious  use  of  manure,  especially  on 
the  heavy  soils,  drainage,  and  proper  tillage  are  all 
factors  which  induce  nitrification,  thereby  also  pre- 
venting denitrification. 

2.      NlTRE-SlCK    SOILS 

This  form  of  sickness,  peculiar  to  certain  Colorado 
soils,  was  carefully  studied  by  Headen x  and  Sackett. 2 
Nitre-sick  soils  are  those  which  contain  such  large 
quantities  of  nitrates  that  they  inhibit  plant  growth. 

1  Headen,  W.  P.,  Colorado  Agr.  Expt.  Sta.  Bui.  155. 

2  Sackett,  W.  G.,  Colorado  Agr.  Expt.  Sta.  Bui.  196:3-39,  1914. 


FIG.  3.     NITRE-SICK  BEET  FIELD,  SHOWING  BARREN  SPOTS. 


Sick  Soils  not  Influenced  by  Parasites  25 

Truck  crops  (fig.  3),  grains,  and  fruit  trees  rapidly 
deteriorate  on  such  lands.  This  condition  occurs  in 
a  variety  of  soils  in  Colorado.  It  is  met  with  in  the 
light  sandy  loams  as  well  as  in  the  heavy  clay  loams, 
on  lowlands  as  well  as  on  hilltops.  It  is  to  be  dis- 
tinguished from  true  alkali  troubles. 

The  distinguishing  characteristic  of  a  nitre-sick 
soil  is  its  brownish-black  wet  appearance.  From 
afar  the  soil  looks  as  if  it  had  been  wetted  with  crude 
oil ;  however  the  soil  is  usually  dry.  Sometimes  the 
soil  may  be  moist  and  slippery,  due  no  doubt  to  the 
presence  of  large  quantities  of  deliquescent  salts. 
Walking  through  such  a  field  produces  a  sensation 
similar  to  that  which  one  would  get  from  walking 
on  cornmeal  or  ashes. 

The  accumulation  of  excessive  amounts  of  nitrates 
in  the  soil  is  due  to  the  activity  of  a  bacterial  soil 
organism,  Azotobacter  chroococcum.  This  organism 
has  the  power  of  fixing  free  nitrogen  from  the  air  and 
depositing  it  in  the  form  of  nitrates  in  the  soil.  The 
conditions  which  favor  this  activity  still  await  study. 
Normally,  soils  contain  from  140  to  150  pounds  of 
nitrates  per  acre  foot.  In  a  nitre-sick  soil,  each  acre 
foot  contains  113,480  pounds,  or  56.74  tons.  With 
such  a  high  concentration  of  nitrate,  it  is  impossible 
for  plants  to  grow.  So  far,  we  know  of  no  methods 
to  reclaim  nitre-sick  soils. 

3.    ACID-SICK  SOILS 

Soils  which  contain  an  excess  of  acid  in  which 
crops  refuse  to  grow,  may  be  termed  acid-sick.  Acids 


26          .  Diseases  of  Truck  Crops 

in  soils  have  a  directly  poisonous  effect  on  plants. 
Soil  acidity  may  be  brought  about  by  the  loss  of  lime 
and  other  bases ;  and  by  the  decomposition  of  organic 
and  inorganic  matter. 

Crops  are  known  to  draw  heavily  on  the  lime  of  the 
soil,  and  thus  increase  the  proportion  of  acidity. 
This  then  is  one  direct  way  of  depleting  the  soil  lime. 
A  ton  of  alfalfa,  for  instance,  is  known  to  take  up  50 
pounds  of  lime.  With  a  yield  of  6  tons  per  acre,  the 
annual  loss  of  lime  per  acre  would  be  2100  pounds. 

Lime  and  other  bases  are  further  lost  from  the 
soil  by  leaching.  The  soluble  carbonates  are  but 
slowly  soluble  in  pure  water.  However,  carbon 
dioxide,  nearly  always  present  in  soils,  changes  the 
calcium  carbonate  into  calcium  bicarbonate,  which 
is  rather  soluble,  and  readily  leaches  out  with  the 
drainage  water. 

Soils  which  are  heavily  manured  are  apt  to  become 
more  acid.  The  decomposition  of  the  organic  matter 
yields  large  quantities  of  carbon  dioxide  which  act  on 
the  carbonate  in  the  manner  above  indicated.  The 
annual  leaching  of  lime  from  soils  varies  from  100  to 
1000  pounds  per  acre. 

In  addition  to  these  causes,  poor  drainage  has  a 
tendency  to  increase  the  soil  acidity.  The  application 
of  ammonium  sulphate  as  a  fertilizer  leads  to  a  devel- 
opment of  acidity  by  the  production  of  sulphuric  acid. 
The  same  is  true  when  muriate  of  potash  is  added. 
In  the  process  of  nitrification  in  which  nitrogen  is 
made  more  available  for  plants,  acids  are  produced. 

Acidity  in  a  soil  is  usually  characterized  by  a  Ian- 


FIG.  4.    EFFECT  OF  LIME. 

a.  to  d.  R  hubarb,  e.  to  h.  New  Zealand  Spinach,  a.  and  6.,  <?.  and/,  both  receiving 
sulphate  of  ammonia,  a.  and  e.  unlimed,  b.  and  /.  limed,  c.  and  d.,  g.  and  A.  both 
received  nitrate  of  soda,  c.  and  g.  unlimed,  d.  and  h.  limed  (after  Hartwell  and 
Damon1*. 


Sick  Soils  not  Influenced  by  Parasites   27 

guid  condition  of  the  growing  crop.  Sorrels,  poverty 
grass,  broomsedge,  cinquefoil,  and  redtop  thrive 
best,  and  are  generally  indicative  of  acid  soils.  Not 
all  truck  crops  are  equally  sensitive  to  soil  acidity. 
Hartwell  and  Damon J  have  determined  the  degree  in 
which  truck  crops  are  benefited  by  the  application  of 
lime  to  an  acid  soil.  As  a  guide  to  the  effect  of  lime 
on  crops,  those  which  seem  to  benefit  most  are  in- 
dicated by  the  number  (3),  lesser  degrees  of  improve- 
ment are  indicated  by  the  numbers  (2)  and  (i). 
Crops  which  tolerate  a  moderate  amount  of  acidity 
are  followed  by  the  figure  (o) ,  and  those  which  thrive 
best  without  lime  by  ( —  i) :  Asparagus  (3),  beans  (o), 
beets  (3),  cabbage  (2),  carrots  (i),  cauliflower  (2), 
celery  (3),  chard  (2),  chicory  (o),  cowpea  (o),  cress 
(o),  cucumber  (i),  eggplant  (2),  endive  (3),  okra  (3), 
horseradish  (2),  kale  (i),  kohlrabi  (i),  leek  (3),  lettuce 
(3),  mustard  (2),  muskmelon  (o),  onion  (3),  parsley  (o), 
parsnip  (3),  pea,  garden  (i),  pepper  (3),  potato  (o), 
radish  (i),  rape  (2),  rhubarb  (3),  sorrel  (  - 1),  spinach 
(3)  (fig-  4&  to  h),  turnip  (o),  watermelon  (  — i). 

Treatment  of  Acid  Soils.  The  best  remedy  known 
is  lime.  Its  effect  is  to  neutralize  the  acidity, 
restoring  the  normal  equilibrium  for  the  activity  of 
the  soil  flora,  and  thus  enabling  the  plant  to  flourish. 
The  amount  of  lime  to  be  used  depends  largely  on 
the  kind  of  soil  and  the  degree  of  its  acidity.  Ac- 
cording to  Blair2  a  loamy  to  a  clay  loam  will  require 

1  Hartwell,  B.  L.,  and  Damon,  S.  C.,  Rhode  Island  Agr.  Expt. 
Sta.  Bui.,  160:  408-446,  1914. 

"Blair,  A.  W.,  New  Jersey  Agr.  Expt.  Sta.  Cir.,  54:  3-11,  1916. 


28  Diseases  of  Truck  Crops 

from  1500  to  2000  pounds  of  burned  lime  per  acre. 
This  is  generally  considered  a  moderate  application. 
For  sands  and  sandy  loams  it  would  be  safe  to  apply 
1000  to  1500  pounds.  If  the  soil  is  known  to  be  very 
acid  or  to  contain  large  amounts  of  organic  matter, 
heavier  application  of  lime  may  be  given.  Lime 
is  sold  as  ground  limestone  or  as  burned  lime.  A  ton 
of  burned  limestone  will  yield  1120  pounds.  If 
enough  water  is  added,  it  will  weigh  1480  pounds. 
If  1 1 20  pounds  of  burned  lime  or  the  1480 
pounds  of  hydrated  lime  are  allowed  to  air  slack, 
the  weight  of  both  will  be  2000  pounds.  Air-slacked 
lime  has  the  same  composition  as  ground  lime- 
stone. In  buying  hydrated  lime  we  do  not  get 
any  better  quality,  but  merely  pay  an  excess  in 
freight  for  the  amount  of  water  it  contains.  The 
cost  of  delivery  should  determine  the  kind  of  lime 
to  buy. 

Wood  ashes  may  often  be  used  instead  of  lime  to 
correct  soil  acidity.  Hardwood  ashes  contain  about 
30  per  cent,  lime  and  60  per  cent,  potash.  Two  and  a 
half  tons  of  good  wood  ashes  are  equivalent  to  one 
ton  of  burned  lime  to  overcome  soil  acidity.  Leached 
ashes  have  lost  their  potash  and  its  lime  is  in  the  form 
of  a  hydrate  or  carbonate. 

Magnesium  lime  which  contains  high  percentages 
of  magnesia  is  not  objectionable  for  use.  In  fact, 
a  ton  of  limestone  which  contains  magnesium  car- 
bonate is  more  effective  on  acid  soils  than  a  ton  of 
limestone  without  magnesium  carbonate.  Lime 
should  be  applied  only  when  the  acidity  of  the  soil 


Sick  Soils  not  Influenced  by  Parasites  29 

requires  it.  After  that  an  additional  application  of 
1000  pounds  of  burned  lime  or  2000  pounds  of  lime- 
stone every  five  years  will  be  desirable.  Should  lime 
be  used  at  more  frequent  intervals,  the  organic  matter 
of  the  soil  will  fast  deplete.  The  saying  that  "lime 
makes  the  father  rich  and  the  son  poor"  is  only  true 
where  the  use  of  lime  is  overdone,  and  not  otherwise. 

4.    MUCK  OR  PEAT  SOILS 

Muck  or  peat  soil  is  sick  because  most  plants 
refuse  to  grow  there  unless  it  is  properly  treated. 
However,  muck  may  be  transformed  into  the  best 
trucking  land.  There  are  States  in  the  Union 
which  possess  muck  lands  by  the  thousands  of  acres. 
Yet  these  are  the  last  to  be  reclaimed.  In 
Europe,  scientists  have  long  concerned  them- 
selves with  the  reclaiming  and  utilization  of  muck 
lands.  Norway,  Sweden,  and  Denmark  have  dealt 
to  a  large  extent  and  with  fair  success  with  the 
problem,  though  much  of  it  still  remains  to  be 
solved.  As  the  term  implies,  peaty  soils  are  those  in 
which  peat  is  the  dominating  constituent.  Peat  is 
always  formed  under  water,  in  swamps  or  marshes, 
undrained  flat  land,  indeed,  any  place  where  water- 
loving  plants  grow  in  abundance.  Most  peat  is 
made  up  mainly  of  sphagnum  and  moss.  Grass  peat 
is  composed  of  swamp  grasses,  sedges,  rushes,  or 
flags.  In  swamps  where  rushes,  sedges,  or  other 
grasses  occur,  peat  formation  is  more  rapid  than 
where  moss  or  sphagnum  grows.  Peat  itself  is 
nothing  more  than  rotten  vegetable  matter.  Com- 


Diseases  of  Truck  Crops 


plete  decomposition  is  impossible,  because  of  the 
absence  of  air  and  the  accumulation  of  plant  acids 
which  contain  antiseptic  properties. 

The  chemical  composition  of  peaty  soils,  as  given 
by  Conner  and  Abbot,1  may  be  seen  in  Table  5. 

TABLE  5 

Chemical  Analyses  of  Different  Types  of  Unproductive 
Black  Soils. 


Kind  of 

Soil 

Substance  determined 

Add 
peat 

Neutral 
peat 

Acid 
peaty 
sand 

Neutral 
peaty 
sand 

Insoluble  &  soluble  silica,  etc. 
Potash  (K2O)  

10.40 
.2^ 

9-OO 
.12 

88.63 
.14 

71-47 
.28 

Lime  (CaO) 

1.86 

^.89 

.08 

S.QI 

Magnesia  (MgO).         

.26 

.52 

.11 

1.  71 

Iron  oxide  (Fe2O3)  ........ 

Aluminum  oxide  (AlzOa)  
Phosphoric  acid  (P3Os)  
Sulphur  trioxide  (SO3)  
Carbon  dioxide  (C02) 

2.87 
•36 

.49 

.20 

4-27 
.40 
.28 
63 

3-25 
.08 
.04 
IO 

5-03 
.21 

4.42 
22 

Volatile  matter. 

8^.16 

81.16 

8.16 

12  l6 

Total  nitrogen 

"O'i(- 

1.82 

-i.ci 

.28 

cy 

Total  potash  (K2O)  
Phosphoric     acid     soluble    in 
N/SHC1  .  . 

•34 
.032 

.26 

.0506 

1.62 

.OO  S8 

1-25 

.0^7 

Total  humus.  .  . 

^0.68 

2S-55 

4.86 

4.72 

Acid  humus.. 

27.74 

1.22 

4.64 

none 

Acidity  in  pounds  calcium  car- 
bonate (CaCOa)  Per  acre  foot 
Hygroscopic  moisture  

I94O.OO 
11.82 

360.00 
18.57 

3500.00 
1.65 

none 

•1.1O 

From  the  table  it  is  evident  that  the  chemical 
composition  is  not  the  same  for  all  peaty  soils.  This 
is  naturally  to  be  expected,  since  no  two  soils  are 

1  Conner,  S.  D.,  and  Abbot,  J.  B.,  Purdue  Agr.  Expt.  Sta.  Bui. 
157  :  vol.  16,  1912. 


Sick  Soils  not  Influenced  by  Parasites   31 

chemically  identical.  In  treating  peaty  soils  it 
should  be  remembered  that  what  applies  to  one  does 
not  generally  apply  to  another. 

Depth  of  Peat  Soils.  Hopkins,  Readhimer,  and 
Fisher1  classify  peaty  soils  according  to  the  depth 
as  follows: 

1.  Soils  in  which  the  very  peaty  material  extends 
three  or  four  feet  at  least,  and  often  to  much  greater 
depths. 

2.  Soils  with  one  to  three  feet  of  peaty  material 
resting  on  deep  sand. 

3.  Soils  with  one  to  three  feet  of  peaty  material 
resting  on  rock,  usually  with  some  inches  of  sandy 
material  between  the  two. 

4.  Soils  with  six  inches  to  three  feet   of   peaty 
material  resting  on  a  clayey  subsoil. 

5.  Soils  with  only  a  few  inches  resting  on  the  sand. 
When  the  peat  is  about  three  feet  in  depth  over  a 

deep  sand  subsoil,  the  land  may  be  lacking  in  potash. 
This  must  then  be  supplied  in  the  form  of  potassium 
salts,  or  of  manure. 

Of  the  many  types  of  peaty  soils,  the  best  for  truck- 
ing are  those  black  deposits  which  have  reached  an 
advanced  state  of  decomposition,  are  of  a  fine  texture, 
and  have  a  high  ash  content.  Brown  peat  of  a 
fibrous  nature  is  not  very  desirable.  Its  physical 
condition  is  such  that  the  water  cannot  be  properly 
controlled. 

Treatment  of  Peat  Soil:    Burning.     The  mistake  is 

1  Hopkins,  C.  G.,  Readhimer,  J.  E.,  and  Fisher,  O.  S.,  Illinois  Agr. 
Expt.  Sta.  Bui.  157  : 95-131,  1912. 


32  Diseases  of  Truck  Crops 

often  made  of  burning  over  peaty  soils  with  a  view 
to  improving  them.  This  practice  cannot  be  too 
strongly  condemned.  It  is  difficult  to  see  where  any 
permanent  benefit  can  result  from  such  treatment. 
Moreover,  burning  destroys  the  nitrogen  and  the 
organic  matter,  which  are  two  valuable  and  expen- 
sive assets  of  such  a  soil.  Should  peat  ever  catch  fire 
accidentally,  pouring  water  or  throwing  soil  on  the 
flames  will  not  smother  them.  In  this  case  it  is  best 
to  dig  an  open  trench  around  the  fire  to  a  depth  of 
moist  earth  and  let  it  burn  itself  out  within  that  limit. 

Drainage.  The  best  method  of  reclaiming  peat 
soils  is  drainage.  This  process  is  not  so  easily  done 
as  on  ordinary  land  because  peat  holds  water 
better  than  ordinary  soils.  Peat  soils  may  be 
drained  if  sufficiently  large  tiles  are  used  and  a 
proper  outlet  is  at  hand.  The  best  results  are  ob- 
tained when  the  tiles  are  laid  in  the  underlying 
muck  or  clay,  but  not  too  deeply  in  the  subsoil. 

Plowing.  The  second  best  method  of  improving 
peat  soils  is  a  proper  working  of  them.  Fall  plowing 
is  to  be  highly  recommended.  The  peat  in  this  case 
is  exposed  to  the  action  of  the  frost,  rain,  and  snow, 
all  of  which  helps  in  the  more  rapid  decay  of  the 
organic  matter.  In  shallow  peaty  layers,  deep 
plowing  is  of  great  value.  This  helps  to  mix  the 
clay  with  the  peat  and  makes  it  more  readily  avail- 
able by  bringing  up  the  potassium  and  the  phos- 
phorus of  the  subsoil.  In  deep  peaty  layers,  deep 
plowing  exposes  a  larger  part  of  the  organic  matter 
to  the  air  and  sunlight.  Rolling  should  never  be 


Sick  Soils  not  Influenced  by  Parasites   33 


practiced  in  very  shallow  layers.  It  is  recommended 
only  where  the  layer  is  over  sixteen  inches  deep. 
Frequent  cultivation  is  also  very  beneficial  and  pro- 
vides aeration  which  favors  a  more  rapid  decay  of 
the  organic  matter.  It  helps  to  keep  down  weeds. 

The  Choice  of  a  Crop.  On  newly  reclaimed  peat 
soils,  the  best  crops  to  plant  are  timothy,  sudan  grass, 
or  alsike  clover,  which  may  be  pastured  to  advantage. 
Peat  soils  cannot  be  surpassed  for  trucking  purposes. 
They  seem  especially  adapted  for  onions,  celery, 
tomatoes,  and  potatoes. 

Use  of  Fertilizers.  The  application  of  certain 
chemical  fertilizers  to  peaty  soils  is  decidedly  bene- 
ficial. The  kind  of  fertilizers  will  depend  largely  on 
the  nature  of  the  crop  grown.  Conner  and  Abbot 
present  interesting  data  on  the  effect  of  fertilizer  on 
onions.  This  is  summarized  in  Table  6. 

TABLE  6 

Results  of  Field  Fertilizer  Tests  with  Onions  on  Various 
Peat  Soils 


Experi- 

Pounds 

Average 

Increase  in  bushels  per  acre 

ment 

fertil- 

unfer- 

izer 

tilized 

No. 

per  acre 

yield 

4-8-10  I 

o-8-io 

4-0-10 

4-8-0 

4-3i 

IOOO 

606.9 

113.0 

124.2 

76.3 

75-5 

43-n 

IOOO 

79.1 

I33-I 

58.0 

49.6 

57-1 

92-21 

IOOO 

307-0 

130.0 

240.0 

145.0 

2O.O 

37-H 

IOOO 

234.0 

332.0 

285.0 

I2O.O 

89.0 

1  4-8-10  formula  indicates  4  per  cent,  nitrogen,  8  per  cent,  phos- 
phoric acid,  and  10  per  cent,  potash  made  from  dried  blood,  acid  phos- 
phate, and  sulphate  of  potash.  Minus  sign  (— )  indicates  decrease. 


34 


Diseases  of  Truck  Crops 


TABLE  6 — (Continued) 


Experi- 
ment 

No. 

Pounds 
fertil- 
izer 
per  acre 

Average 
unfer- 
tilized 
yield 

Increase  in  bushels  per  acre 

4-8-10 

o-8-i  o 

4-0-10 

4-8-0 

-64.6 
25.0 
47.6 

145.5 
49.0 

$12.28 

12.22 

37-15 
43-21 
57-n 
57-1  la 
Average 

1000 
1000 
1000 

500 

613.0 
628.0 
394-2 
372.8 
404.4 

73-7 
o.o 
89.0 
171.7 
130.3 

-27.1 
75-0 
49.1 
178.6 

122.8 

127.1 
—30.0 

55-2 
128.6 
84.0 

Cost  of  fertilizer 
Average  profit  pe 

$17.34 

$  9.56 
51.84 

$12.84 
29.16 

r  acre.              47-8  1 

We  have  as  yet  no  definite  data  on  the  effect  of  lime 
on  peaty  soils.  Those  in  charge  of  the  development 
of  peaty  soils  caution  against  using  it  too  freely.  Of 
the  forms  to  use,  ground  limestone  or  marl  are  per- 
haps the  best  kinds  to  apply.  The  amount  to  use 
will  vary  from  one  to  four  tons,  depending  largely  on 
the  acidity  of  the  soil.  Too  much  lime  tends  to  de- 
stroy the  nitrogenous  compounds,  and  encourages 
serious  plant  diseases. 

5.    ALKALI-SICK  SOILS 

The  alkali  problem  is  even  of  more  widespread 
concern,  as  it  affects  nearly  all  irrigated  districts 
of  the  arid  and  semi-arid  regions  of  the  United 
States.  An  alkali-sick  soil  is  one  which  contains 
an  excess  of  accumulated  soluble  salts  which  are 
injurious  to  plant  growth.  For  convenience, 
alkali  soils  are  divided  into  black  and  white.  The 
black  alkali  lands  are  known  to  contain  sodium 
carbonate  or  washing  soda  as  the  essential  salt.  The 


Sick  Soils  not  Influenced  by  Parasites   35 


latter  does  not  act  so  much  on  the  soil  as  on  the  or- 
ganic matter,  turning  it  black.  This  black  material 
is  always  found  on  the  surface  with  the  salts.  The 
blackening  of  the  soil,  however,  is  not  always  an 
indication  of  black  alkali.  Many  dark  spots  are 
found  to  contain  the  white  alkali.  Moreover,  soils 
which  contain  little  or  no  organic  matter  may  con- 
tain large  quantities  of  sodium  carbonate  and  never 
turn  black.  The  white  alkali  in  reality  is  not  a  true 
alkali.  The  salts  found  in  it  are  sodium  chloride  or 
table  salt,  calcium  sulphate  or  gypsum,  sodium  sul- 
phate, magnesium  sulphate  or  Epsom  salt.  In 
addition  to  these  may  be  found  salts  of  potassium. 
Table  7,  taken  from  Harris, x  shows  a  comparative 
study  of  the  total  soluble  salts  which  are  found  to  be 
injurious  to  plants. 

TABLE  7 

Summary  of  Total  Soluble  Salts,  Chlorides,  Carbonates, 

and  Sulphates  in  Alkali  Soils.     Average  to  a  Depth 

of  Four  Feet,  Parts  per  Million  of  Dry  Soil. 

Parts  of  field  producing  best  crop 


Total 

Counties 

Soluble 

Chlorides 

Carbonates 

Sulphates 

Salts 

Boxelder 

4,806 

1,485 

1,983 

711 

Salt  Lake 

2,440 

545 

858 

2,334 

Millard 

10,852 

640 

1,418 

9,795 

Cache 

5,792 

i,573 

1,515 

2,539 

•x  Harris,  F.  S.,  Utah  Agr.  Expt.  Sta.  Bui.,  145  13-21,  1916. 


Diseases  of  Truck  Crops 

TABLE  7 — (Continued) 


Parts  of  field  producing  medium  crop 


Total 

Counties 

Soluble 

Chlorides 

Carbonates 

Sulphates 

Salts 

Boxelder 
Salt  Lake 

7,075 
4,228 

3,021 
875 

1,727 
792 

543 
i,  812 

Millard 
Cache 

18,325 
17,218 

3,077 
2,541 

1,271 

888 

13,238 
13,126 

Parts  of  field  where  no  crop  would  grow 


Boxelder 
Salt  Lake 

10,079 
6,938 

6,767 
2,045 

1,874 
689 

i,i54 
3,636 

Millard 

21,488 

6,289 

1,875 

13,304 

Cache 

30,148 

3,585 

795 

23,027 

Origin  of  Alkali  Soils.  Soils  are  formed  through 
the  disintegration  of  rocks  due  to  various  agencies 
such  as  weather,  water,  chemicals  and  organic 
matter,  and  the  action  of  the  soil  flora.  In  this  pro- 
cess, substances  are  released,  some  of  which  are  in- 
soluble while  others  are  readily  soluble  in  water. 

Although  in  moist  and  cold  climates  the  more 
rapid  decomposition  of  rocks  leaves  more  salt  de- 
posits in  the  soil,  the  abundant  rainfall  washes  out 
these  salts,  which  are  carried  off  by  the  streams  and 
rivers  to  the  ocean.  This  is  not  the  case  in  arid 
regions  where  the  salts  are  gradually  allowed  to 
accumulate.  Much  of  the  rain  in  the  arid  regions 
does  not  find  an  outlet  in  streams,  but  accumulates 
in  the  lower  regions,  where  the  water  finally  evapo- 


Sick  Soils  not  Influenced  by  Parasites   37 

rates,  leaving  a  deposit  of  salts.  This  then  is  one  way 
in  which  alkali  spots  are  formed.  Another  source  of 
alkali  formation  is  through  the  decomposition  of 
volcanic  rocks.  This  condition  is  found  in  some  parts 
of  New  Mexico.  Another,  and  by  far  the  most  im- 
portant, source  of  alkali  formation  is  through  capil- 
larity and  evaporation.  This  occurs  when  the  water 
accumulated  in  the  soil  is  insufficient  to  raise  the 
water  table  high  enough  to  permit  evaporation.  The 
condition  which  most  favors  such  an  accumulation 
of  water  is  a  bed  or  layer  of  a  clayey  character  which 
prevents  the  percolation  of  water  downwards,  below 
a  soil  which  does  not  have  sufficient  lateral  drainage. 
The  source  of  the  water  may  be  springs,  or  the  perco- 
lation of  surface  rainwater,  and  in  irrigated  regions, 
leaky  canals  or  over-irrigation.  The  depth  of  the 
water  table,  where  capillarity  becomes  a  source  of 
trouble,  is  about  three  feet.  As  all  soil  water  contains 
diluted  salts,  continual  evaporation  will  leave  alkali 
spots  or  beds.  To  realize  further  what  the  alkali 
accumulation  means,  Tinsley1  has  worked  out  some 
interesting  figures. 

"Suppose  an  acre  of  land,  with  the  water  table 
within  less  than  two  feet  of  surface,  and  that  the 
amount  of  water  evaporated  from  the  surface  in  a 
year  was  enough  to  cover  the  acre  to  a  depth  of  one 
foot,  which  the  writer  considers  a  low  estimate  for  a 
bare  soil.  Suppose  further  that  when  it  reached  the 
surface,  the  water  carried  100  parts  of  soluble  matter 
in  100,000  parts  of  water,  which  is  about  the  salt 

.     *  Tinsley,  J.  D.,  New  Mexico  Agr.  Expt.  Sta.  Bui.  42  :  3-31,  1902. 


38  Diseases  of  Truck  Crops 

content  of  the  best  irrigating  waters  in  the  Roswell 
district.  This  would  give  43,560  cubic  feet  of  water 
on  the  acre,  which  would  weigh  about  2,720,000 
pounds,  and  would  leave  on  evaporation  2720  pounds 
of  salt,  about  one  and  one  half  tons. 

"This  would  amount  to  an  addition  of  .07  per  cent. 
of  salt  to  the  surface  foot  of  that  acre  per  year.  If 
this  were  continued  about  seven  years,  and  none  of 
the  salts  were  removed,  the  amount  added  would  be 
about  .5  per  cent,  in  the  first  foot  of  soil,  which  is 
more  per  foot  than  cultivated  plants  could  usually 
withstand.  Under  actual  conditions,  it  is  probable 
that  more  than  one  and  one  half  tons  of  salts  per  acre 
per  year  are  carried  to  the  surface  in  many  cases,  but 
the  rain  washes  a  portion  of  them  back  and  they  are 
distributed  to  a  greater  depth  than  one  foot." 

Effect  of  Alkali  on  Plant  Growth.  Plants  can 
stand  the  baneful  effect  of  alkali  only  to  a  limited 
degree.  The  damage  is  always  confined  to  the  stem 
end.  Here  the  epidermis  turns  brown  for  half  an 
inch  or  more,  gradually  tearing  away  in  a  girdling 
fashion.  This  results  in  the  collapse  and  death  of  the 
plant,  which  assumes  a  corroded  appearance.  The 
physiological  effect  of  alkali  is  to  plasmolize  the  cell 
contents  of  the  bark. 

Crops  Adapted  to  Alkali  Lands.  Unlike  peaty 
lands,  alkali  soils  are  adapted  to  very  few  trucking 
crops.  Sugar  beets,  carrots,  and  artichokes  seem  to 
thrive  fairly  well  in  such  soils.  Irish  potatoes  will 
thrive  well  in  soils  which  do  not  contain  more  than 
18,400  pounds  of  alkali  per  acre,  of  which  4000 


Sick  Soils  not  Influenced  by  Parasites   39 

pounds  may  be  carbonate  of  soda,  and  6880  pounds 
common  salt.  Broccoli,  chard,  fennel,  and  sweet  corn 
will  thrive  fairly  well  in  lands  containing  up  to  a  total 
of  3720  pounds  of  alkali  per  acre. 

How  to  Reclaim  Alkali  Soils.  We  have  seen  that 
the  accumulation  of  alkali  in  a  soil  is  often  brought 
about  by  the  evaporation  of  water  which  is  charged 
with  mineral  salts.  To  obviate  this  it  is  evident 
that  the  evaporation  must  be  counteracted.  Good 
surface  cultivation  will  establish  a  dry  surface 
mulch  and  prevent  the  rise  of  water  to  the  upper 
level,  thereby  preventing  evaporation.  Tillage  to 
be  effective  must  be  started  early,  because  then, 
large  quantities  of  salt  would  be  carried  into  the 
subsoil  by  the  spring  rains.  If  the  crop  is  started 
early,  it  may  be  forced  to  maturity  before  the  effect 
of  alkali  can  make  itself  felt  on  the  plants.  Tillage, 
however,  will  afford  only  temporary  relief,  as  it  will 
not  remove  the  salts  from  the  soil.  Drainage  on  the 
other  hand  affords  permanent  relief.  The  land  is 
first  flooded,  preferably  in  the  winter,  and  then  the 
water  which  is  now  laden  with  soluble  salts  is  removed 
by  a  system  of  drainage.  Tile  drainage,  while  more 
expensive  in  its  initial  cost,  is  cheapest  in  the  long 
run.  Such  a  system  when  laid  down  permanently 
will  prevent  the  further  accumulation  of  salts. 

The  application  of  manure  or  straw  to  alkali  land 
often  brings  marked  relief.  Many  a  barren  spot  has 
been  reclaimed  by  this  method.  The  beneficial 
action  of  manure  or  straw  is  easily  accounted  for. 
Both  of  these  tend  to  loosen  the  surface  soil,  thereby 


40  Diseases  of  Truck  Crops 

acting  as  a  surface  mulch,  and  indirectly  preventing 
evaporation.  They  may  also  stimulate  young  plants 
to  more  rapid  growth,  enabling  them  to  withstand 
the  action  of  alkali.  Young  plants  are  much  more 
sensitive  to  alkali  than  older  ones.  The  older  plants 
of  cantaloupes,  for  instance,  are  far  more  resistant  to 
alkali  than  the  young  seedlings. 


CHAPTER   III 

SOIL  SICKNESS  DUE  TO  THE  PRESENCE  OF  PARASITES 
HARMFUL  TO   PLANTS 

WHEN  a  soil  is  sick  because  its  beneficial  bacteria 
do  not  perform  their  functions  properly,  or  because 
of  abnormalities  in  its  chemical  properties,  careful 
treatment  and  proper  cultural  methods  will  restore 
it  to  health.  But  when  a  soil  becomes  sick  and  un- 
productive because  parasitic  forms  gain  a  foothold 
there,  much  greater  skill  and  knowledge  are  required 
to  cope  with  the  problem.  Its  solution  is  of  the 
greatest  economic  importance  to  the  trucker  and 
gardener. 

Parasitic  fungi  finding  their  way  in  a  soil  do  not 
necessarily  interfere  with  the  work  of  the  beneficial 
bacteria,  such  as  the  ammonifiers  and  nitrifiers,  for 
instance.  Neither  do  they  always  influence  the 
chemical  or  physical  nature  of  the  soil.  They  attack 
directly  the  crop  itself.  Of  the  numerous  parasites 
rendering  soils  unproductive,  we  will  consider  here 
only  two  types. 

I.    SOIL  SICKNESS  DUE  TO  PARASITIC  FUNGI. 
Fungi  which  produce  DAMPING  OFF  in  seedlings. 

41 


42  Diseases  of  Truck  Crops 

Fungi  which  produce  damping  off  as  well  as  WILTS, 
BLIGHTS,  or  ROTS  in  plants. 

DAMPING  OFF 
Caused  by  Pythium  de  Baryanum  Hesse. 

This  disease  is  very  familiar  to  every  grower  of 
plants.  The  trouble  is  peculiar  to  seedlings  or  very- 
tender  plants.  It  is  prevalent  in  the  greenhouse,  the 
hotbed,  the  cold  frame,  and  frequently  also  in  the 
field.  The  trouble  is  induced  by  the  presence  of 
definite  parasitic  fungi  in  the  soil.  They  thrive  best 
when  the  land  is  continually  damp,  and  the  at- 
mospheric temperature  comparatively  high.  Damp- 
ing off  is  also  favored  by  thick  sowing  and  too  much 
shade  in  the  seed  bed. 

Symptoms  of  Damping  Off.  Every  experienced 
trucker  knows  the  disease  when  he  sees  it.  Seedlings 
freshly  damped  off  are  soft  and  water-soaked  at  the 
base  of  the  stem.  If  they  are  pulled  they  often  break 
off  easily.  A  more  careful  examination  shows  that 
the  root  system  is  entirely  decayed  by  this  time,  al- 
though the  upper  part  of  the  stem  and  leaves  may 
still  be  green,  possibly  also  fresh.  The  degree  of 
prostration  in  the  seedlings  is  regulated  by  the 
amount  of  moisture  in  the  soil.  If  the  amount  of 
moisture  is  slight,  the  seedlings  will  be  flabby  and 
wilted  before  they  topple  over.  With  a  high  mois- 
ture content,  they  are  more  firm,  but  become  pros- 
trate as  soon  as  infection  starts  in.  Damping  off 


FIG.  5.     PYTHIUM  DEBARYANUM. 

.  Mycelium,  6.  conidiophore  bearing  con- 
idia,  c.  germinating  conidium,  d.  fertil- 
ized pogonium  and  adjoining  empty 
antheridium,  e.  oospore. 


Soil  Sickness  Due  to  Parasites        43 

usually  begins  in  spots  in  the  seed  bed  or  in  the  field 
and  then  may  spread  in  every  direction. 

The  Organism.  Pythium  de  Baryanum  was  first 
named  and  described  by  Hesse  in  1874.  Ward1 
found  it  to  be  a  very  prevalent  parasite  in  the  garden 
soils  of  Europe.  In  America  the  fungus  was  first 
recognized  by  Atkinson2  as  of  great  economic  im- 
portance. Pythium  de  Baryanum,  when  examined 
under  a  compound  microscope,  is  seen  to  be  made 
up  of  coarse,  non-septate,  highly  granular,  irregular 
branched  hyaline  vegetative  threads  or  mycelium 
(fig.  5  a).  The  younger  threads  are  more  finely 
granular,  the  oldest  ones  are  coarsely  granular  or 
more  often  empty.  These  threads  penetrate  the 
cells  of  the  host,  where  they  obtain  food. 

Pythium  de  Baryanum  does  not  often  fruit  freely 
on  the  dead  host.  The  fruiting  is  better  observed 
when  it  is  grown  in  a  pure  culture.  Under  normal 
conditions  the  fungus  produces  two  forms  of  spores, 
conidia  (fig.  5  b)  and  oogonia  (fig.  5  d,  e).  The 
summer  spores,  or  conidia,  are  swellings  formed  at 
the  tip  of  the  hyphae.  These  swellings  readily  break 
off  from  the  mother  threads  and  germinate  by  send- 
ing out  a  slender  tube  (fig.  5  c) .  This  tube  penetrates 
the  seedling  tissue,  where  it  grows  and  develops  and 
after  due  incubation  reproduces  the  disease.  The 
oospore  or  sexual  spore  is  the  stage  which  is  most 
commonly  found.  The  female  oogonium  first  devel- 

1  Ward,  M.,  Quart.  Jour.  Micros.  Soc.,  New  Ser.  22  :  487,  1883. 
a  Atkinson,  G.  F.,  New  York  (Cornell)  Agr.  Expt.  Sta.  Bui.  94  : 
233-272,  1895. 


44  Diseases  of  Truck  Crops 

ops  as  a  terminal  enlargement  which  is  cut  off  by  a 
septum  from  the  mother  thread.  Next  or  adjacent 
to  it  a  slender  tube  is  cut  off  from  the  mycelium  by  a 
septum.  This  tube  now  performs  the  function  of  the 
male  sexual  organ  and  is  known  as  antheridium. 
The  latter  then  comes  into  close  contact  and  empties 
all  its  content  into  the  oogonium  (fig.  5  d) .  Fertiliza- 
tion thus  takes  place,  and  a  mature  egg  or  oospore 
or  winter  resting  spore  is  formed  (fig.  5  e). 

The  latest  investigations  have  not  yet  disclosed 
whether  or  not  Pythium  de  Baryanum  is  carried  over 
from  year  to  year  by  its  oospores.  It  is  apparently 
able  to  propagate  itself  indefinitely  by  its  vegetative 
mycelium.  The  seedlings  of  the  following  truck  crops 
are  subject  to  damping  off  by  Pythium :  Beans,  beets, 
cabbage,  cauliflower,  endive,  lettuce,  pumpkin,  tom- 
ato, and  turnip. 

Of  the  other  fungi  which  are  capable  of  producing  a 
damping  off  in  seedlings  may  be  mentioned;  Sdero- 
tinia  liber tiana  Fckl.,  Phoma  solani  Halst.,  Colle- 
totrichum  sp.,  Fusarium  sp.;  Sderotium  Rolfsii  Sacc., 
and  Rhizoctonia  solani  Kiihn.  The  first  five  will  be 
taken  up  separately  in  connection  with  the  study  of 
their  respective  hosts  (see  pages  45, 46,  143,  305,  324). 

OTHER  SOIL  DISEASES 

We  have  seen  that  Pythium  de  Baryanum  is  most 
active  as  a  disease  on  young  seedlings.  Other  fungi, 
however,  may  attack  not  only  seedlings,  but  also 
older  plants,  in  various  stages  of  development.  As 


FIG.  6.     RHIZOCTONIA. 

a.  Rhizoctpnia  cankers  on  stems  of  young  bean  plants,  b.  young  growing  hyphae 
of  Rhizoctonia,  c.  young  barrel  shaped  cells  which  compose  the  sclerotia  of  Rhizoc- 
tonia, d.  older  and  empty  barrel  shaped  cells  of  sclerotia  (a.  to  d.  after  Peltier). 


Soil  Sickness  Due  to  Parasites        45 

a  guide  to  the  trucker  and  gardener,  we  shall  consider 
two  typical  soil  diseases,  one  which  produces  root 
rot,  the  other  wilt  only. 

ROOT  ROT 
Caused  by  Rhizoctonia  solani  Kuhn. 

This  fungus  is  of  great  economic  importance  be- 
cause of  its  widespread  distribution.  It  is  capable 
of  producing  a  damping  off  on  a  variety  of  seedlings, 
as  well  as  of  attacking  older  and  mature  plants. 

Symptoms.  The  symptoms  of  Rhizoctonia  wilt 
do  not  differ  materially  from  those  produced  by 
Pythium  de  Baryanum.  On  older  plants  however 
Rhizoctonia  produces  cankers  or  deep  lesions  which 
are  very  characteristic  (fig.  6  a).  These  are  formed 
on  the  roots  as  well  as  on  the  base  of  the  stem. 
The  lesions  are  reddish  brown  and  extend  into  the 
cortical  or  vital  layer  as  well  as  into  the  woody  tissue. 
There  is  perhaps  no  other  parasitic  fungus  which  is 
so  widespread  and  capable  of  attacking  such  a  vari- 
ety of  hosts  as  Rhizoctonia.  The  work  of  Peltier1 
shows  that  the  following  truck  crops  are  susceptible 
to  Rhizoctonia:  Beet,  bean,  cabbage,  cauliflower, 
celery,  cowpea,  cucumber,  cress,  eggplant,  horse- 
radish, lettuce,  muskmelon,  okra,  pepper,  radish, 
squash,  sweet  potato,  garden  pea,  parsnip,  potato, 
and  tomato. 

The  Organism.     In  1828  Duhamel  described  Rhi- 

*  Peltier,  G.  L.,  Illinois  Agr.  Expt.  Sta.  Bui.  189:  283-391, 1916. 


46  Diseases  of  Truck  Crops 

zoctonia  for  the  first  time.  In  the  United  States  the 
first  extended  account  of  the  fungus  was  given  by 
Pammel. x  Many  other  excellent  accounts  by  Amer- 
ican workers  have  appeared  from  time  to  time,  to 
which  we  shall  have  occasion  to  refer  later. 

The  genus  Rhizoctonia  includes  several  forms  of 
sterile  fungi,  all  of  which  are  distinguished  by  their 
manner  of  growth  in  pure  culture,  and  by  their 
mycelium  form.  Young  hyphae  of  R.  solani  Kuhn 
are  at  first  hyaline,  then  deepen  in  color  from  a  yellow- 
ish to  a  deep  brown.  The  young  branches  are  some- 
what narrowed  at  their  point  of  union  with  the  parent 
hypha  and  grow  in  a  direction  alrhost  parallel  to  each 
other  (fig.  6  b).  A  septum  is  also  laid  down  at  a 
short  distance  from  the  point  of  union  with  the  par- 
ent mycelium.  There  is  another  form  of  mycelium 
which  is  made  up  of  barrel-shaped  cells,  each  of  which 
is  capable  of  germinating  like  a  spore  (fig.  6  c,  d).  In 
pure  cultures  R.  solani  produces  sclerotia,  which  are  at 
first  soft,  whitish,  and  later  become  hard  and  dark. 
The  fungus  is  carried  over  from  year  to  year  as  scler- 
otia which  are  able  to  withstand  the  effect  of  heat, 
cold,  drought,  or  moisture. 

PARASITIC  SOIL  FUSARIA 

Next  in  importance  to  Rhizoctonia  is  a  group  of 
fungi  which  belong  to  the  genus  Fusarium.  Lands 
infected  with  these  species  of  fungi  become  unfit  for 
cabbage,  potatoes,  tomatoes,  etc.,  causing  great  finan- 

1  Pammel,  L.  H.,  Iowa  Agr.  Expt.  Sta.  Bui.  15:  244-251,  1891. 


FIG.  7.     FUSARIUM  WILT. 

a  Early  stage  of  Fusarium  wilt  of  sweet  potato,  b.  sweet  potato  hill  killed 
by  Fusarium  wilt,  c.  spores  of  Fusarium  batatatis,  d.  spores  of  Fusarium  hyper* 
oxysporum,  e.  chlamydospores  of  Fusarium  (c.  and  d.  after  Harter). 


Soil  Sickness  Due  to  Parasites        47 

cial  losses  to  the  trucker.  We  will  take  up  the  specific 
troubles  in  studying  each  of  these  crops  respectively. 
As  an  illustration  of  a  typical  Fusarium-sick  soil  we 
will  consider  the  wilt  of  sweet  potatoes. 

WILT  OR  YELLOWS  OF  THE  SWEET  POTATO 

Caused  by  Fusarium  batatatis  Woll.  and  F.  hyper- 
oxysporum  Woll. 

Symptoms.  The  first  indication  of  sweet  potato 
wilt  is  a  slight  difference  in  the  color  of  the  foliage 
in  the  affected  plants.  The  leaves  become  dull,  then 
yellow  between  the  veins  and  slightly  puckered ;  this 
is  followed  by  the  wilting  of  the  affected  vines  (fig. 
7  a).  If  one  of  these  vines  be  split  open  at  the  stem 
end,  the  interior  of  the  woody  portion  will  be  found 
blackened.  All  parasitic  soil  Fusaria  invade  the 
interior  of  the  water  or  fibro- vascular  bundles  which 
are  situated  in  the  woody  tissue  of  the  stem.  Wilting 
and  death  of  the  plant  follow  (fig.  7  b). 

The  morphology  of  Fusarium  is  identical  in  many 
species.  They  differ  only  from  a  pathological  point 
of  view,  and  in  peculiarity  of  certain  colors  produced 
on  media  in  pure  cultures.  Pathologically,  many  of 
the  species  are  distinct.  The  Fusarium  of  the  sweet 
potato  wilt  cannot,  as  far  as  we  know,  attack  potatoes, 
tomatoes,  or  any  other  host.  This  is  similarly  true 
for  the  Fusarium  which  produces  a  wilt'on  tomatoes, 
etc.  The  mycelium  of  Fusarium  is  hyaline,  septate, 
and  branched.  The  spores  are  sickle-shaped  and 


48  Diseases  of  Truck  Crops 

very  characteristic  (fig.  7  c,  d).  Some  Fusaria  also 
produce  chlamydospores  or  resting  spores,  by  which 
the  fungus  is  carried  over  winter  (fig.  7  e).  As  far  as 
we  know  the  wilt-producing  Fusaria  do  not  form  a 
winter  or  ascus  stage.  They  are  carried  over  as 
mycelium,  or  chlamydospores,  in  dead  plants  and  in 
the  soil. 

2.    SOILS  RENDERED  SICK  BY  CERTAIN  FORMS 
OF  ANIMAL  LIFE 

The  present  discussion  deals  with  the  root  knot,  a 
disease  produced  by  a  little  worm  generally  known  as 
nematode,  or  eel  worm. 

ROOT  KNOT 
Caused  by  Heterodera  radicicola  (Greef)  Mull. 

Root  knot  is  most  prevalent  in  light  soils.  This, 
however,  does  not  exclude  it  from  heavier  lands  where 
it  may  sometimes  be  found.  The  trouble  is  most 
widespread  in  the  Southern  States,  where  the  winter 
is  mild.  In  unprotected  places  in  the  North  its 
numbers  are  probably  greatly  reduced  each  winter. 
The  annual  financial  losses  from  this  disease  are 
staggering  in  extent.  With  proper  culture  and  fer- 
tilization, however,  a  crop  may  be  produced  with 
practically  very  little  loss  where  neglect  would  have 
caused  a  total  failure.  This  is  especially  true  under 
greenhouse  conditions. 


FIG.  8.     NEMATODE  ROOT  KNOT. 

a.  Root  knot  of  Irish  potato,  b.  root  knot  of  onion,  c.  root  knot  of  parsnip,  d. 
egg  of  nematode,  Heterodera  radicicola,  e.  young  female  worm,  /.  half-grown  female 
worm,  g.  young  male  worm,  h.  matured  male  worm  ready  to  emerge  from  old  body 
covering,  ».  matured  female  worm  (d.  to  *.  greatly  enlarged,  after  Stone  and  Smith). 


Soil  Sickness  Due  to  Parasites        49 

Symptoms.  The  disease  is  characterized  by  a 
swelling  on  the  roots,  showing  itself  in  small  knots 
formed  either  singly  or  in  pairs,  or  in  strings,  giving 
the  affected  root  a  beaded  appearance  (fig.  8  a,  b). 
Sometimes,  however,  the  swellings  are  so  large  that 
they  may  be  mistaken  for  the  root  nodules  (fig.  8  c) 
of  legume  plants,  which  occur  normally  in  great 
abundance.  Infested  plants  usually  linger  for  a  long 
time,  but  they  can  be  distinguished  by  a  thin  growth 
and  yellow  sickly  looking  leaves  and  stems. 

Distribution.  The  eelworm  seems  to  be  of  world- 
wide distribution,  being  found  in  Europe,  Asia, 
Australia,  and  both  North  and  South  America. 
And  yet,  there  are  many  localities  in  which  this  pest 
has  never  been  known. 

Life  History.  The  eelworm  is  a  very  minute  worm, 
seldom  exceeding  one  twenty-fifth  of  an  inch  in 
length.  It  is  semi  transparent,  so  that  it  cannot  be 
easily  detected  by  the  naked  eye.  In  searching  for  the 
eelworm,  break  a  fresh  knot.  Close  examination  will 
reveal  two  types  of  worms:  a  spindle-shaped  worm, 
the  male  (fig.  8  g,  h),  and  a  pearly  white  pear-shaped 
organism,  the  female  (fig.  8  e,  f),  firmly  embedded  in 
the  gall  tissue.  The  female  is  very  prolific,  depositing 
no  less  than  400  to  500  eggs  during  her  lifetime. 
The  eggs  are  whitish  (fig.  8  d),  semi  transparent 
bean-shaped  bodies,  and  too  small  to  be  noticed 
without  the  aid  of  a  magnifying  glass.  The  time 
which  elapses  until  the  eggs  hatch  depends  largely 
upon  weather  conditions.  In  warm  days  the  eggs 
hatch  sooner  than  in  cold  days.  Upon  hatching,  the 


50  Diseases  of  Truck  Crops 

young  larvae  either  remain  in  the  tissue  of  the  host 
plant  in  which  they  have  emerged,  or,  as  is  more  often 
the  case,  leave  the  host  and  enter  the  soil.  This  is 
the  only  period  during  which  the  worms  move  about 
to  any  great  extent  in  the  soil,  where  they  either 
remain  for  some  length  of  time  or  immediately  pene- 
trate another  root  of  the  host.  The  nematodes  in 
most  cases  become  completely  buried  in  the  root 
tissue,  establishing  themselves  in  the  soft  cellular 
structure  which  is  rich  in  food.  The  head  of  the 
worm  is  provided  with  a  boring  apparatus  consisting 
of  a  sharply  pointed  spear,  located  in  the  mouth. 
This  structure  not  only  aids  it  in  getting  food  but  is 
also  valuable  in  helping  the  young  worms  to  batter 
through  the  cell  walls  before  becoming  definitely 
located.  The  two  sexes  during  the  development  are 
undistinguishable  up  to  fifteen  or  twenty  days,  both 
being  spindle-shaped.  In  the  molting  or  shedding 
of  the  skin,  there  is  a  marked  change  in  the  case  of 
the  female,  especially  in  the  posterior  region  of  the 
body,  which  no  longer  possesses  a  tail-like  appendage. 
Fertilization  occurs  soon  after  this  molt,  and  many 
radical  changes  occur  in  the  shape  and  structure  of 
the  organization  of  the  worm.  The  fertilized  female 
increases  rapidly  in  breadth  and  becomes  a  pearly 
white  flask-  or  pear-shaped  individual  (fig.  8  i). 
At  this  stage  it  is  far  from  being  wormlike  and  may, 
therefore,  be  overlooked  by  one  unfamiliar  with  the 
life-history  of  the  eel  worm.  The  adult  male  is  much 
like  that  of  the  young  female  larvse,  being  spindle- 
shaped  in  outline.  The  male  does  not  cause  as  much 


Soil  Sickness  Due  to  Parasites        51 

damage  to  the  root  tissue  as  the  female,  and  its  pur- 
pose in  life  seems  to  be  only  that  of  fertilizing  the 
female,  for  after  this  function  has  been  performed, 
it  is  quite  probable  that  the  male  worm  takes  no 
more  food. 

Omnivorous  Nature  of  the  Eelworm.  There  are 
almost  five  hundred  species  of  plants  known  to 
suffer  from  the  eelworm.  This  number  includes 
all  the  important  families  of  the  flowering  plants. 
According  to  Bessey1  the  following  are  among  the 
plants  subject  to  root  knot: 

a.  Truck  Crops.     Asparagus,  bean,  beet,  cabbage, 
carrot,  cauliflower,  celery,  chicory,  cucumber,  dill, 
eggplant,  endive,  gourd,  Jerusalem  artichoke,  leek,  let- 
tuce, muskmelon,  mustard,  okra,  onion,  parsley,  pars- 
nip, pea,  pepper,  potato,  pumpkin,  radish,  rutabaga, 
salsify,  shallot,  Spanish  oyster  plant,  spinach,  squash, 
sweet  potato,  tomato,  turnip,  watermelon,  yam. 

b.  Garden  Weeds.     Birdsfoot  trefoil,  burdock,  car- 
petweed,  dandelion,  dead  nettle,  Florida  beggarweed, 
horse   nettle,  lamb's-quarters,  mayweed,  milkweed, 
nightshade,  pigweed,  plantain,  pokeweed,  ribgrass, 
shepherd 's-purse,    sheep    sorrel,   snow   thistle,   wild 
morning-glory. 

From  the  above  large  list  of  susceptible  hosts,  it 
is  evident  that  the  trucker  cannot  afford  to  permit 
infestation  of  his  land.  Once  a  soil  becomes  sick 
because  of  the  presence  of  eelworm  there  is  very- 
little  range  left  in  the  choice  of  a  crop. 

1  Bessey,  E.  A.,  U.  S.  Dept.  Agr.  Bureau  PI.  Ind.  Bui.  217  : 
7-89,  1911. 


52  Diseases  of  Truck  Crops 

SOIL-INFESTING  INSECTS 

Soils  infested  with  insect  pests  are  as  sick  as  when 
infested  with  eel  worm  or  parasitic  fungi.  The 
trucker,  in  sowing  his  seed,  has  often  great  difficulty 
in  obtaining  a  good  and  even  stand.  The  frequent 
resowings  invariably  result  in  late  crops,  and  this 
means  heavy  money  losses.  Frequently  the  stand 
is  reduced  by  fifty  per  cent,  in  spite  of  the  many 
resowings.  The  cause  of  this  may  be  traced  to  the 
presence  in  the  soil  of  certain  insect  pests.  Among 
those  dreaded  most  by  the  trucker  and  gardener  are : 
Cutworms  (A gratis  sp.),  (Lycophotiasp.),  (Peridroma 
sp.),  wire  worms  (Melanotus  sp.),  and  white  grubs 
(Phyllophaga  sp.). 


CHAPTER  IV 

METHODS  OF  TREATING   SICK  SOILS 

^  DAMPING  OFF,  whether  induced  by  Pythium,  Rhi- 
zoctonia,  or  any  other  parasitic  organism,  is  usually 
confined  to  seedlings  in  the  seed  bed,  under  cover  or 
in  the  open.  The  loss  of  seedlings  not  only  means  a 
waste  of  seeds,  but  it  also  results  in  late  crops. 
Growers  are  usually  in  the  habit  of  using  the  same 
soil  injthe  seed  bed,  year  in  and  year  out.  This  prac- 
tice cannot  be  encouraged,  since  contamination  of 
the  seed-bed  soil  is  bound  to  take  place.  The  dis- 
ease-producing organisms  are  usually  brought  in 
with  the  manure.  A  number  of  truckers  make  it  a 
practice  to  empty  their  beds  and  fill  them  with  fresh 
soil.  This,  unfortunately,  is  not  always  a  safe 
method,  for  the  reason  that  the  new  soil  too  may 
be  contaminated,  or  that  it  may  become  infected 
as  soon  as  it  is  placed  in  the  bed  previously  con- 
taminated. Sick  seed-bed  soils  may  be  freed  from 
damping  off  in  various  ways. 

Formaldehyde.  When  steam  sterilization  is  not 
feasible  because  of  the  absence  of  a  steam  boiler,  the 
formaldehyde  treatment  is  the  next  best.  With  this 
treatment  we  may  control  Fusarium,  Rhizoctonia, 

53 


54  Diseases  of  Truck  Crops 

and  Pythium  in  infected  beds.  It  is  doubtful, 
however,  if  this  treatment  will  entirely  eradicate  eel- 
worms  from  infested  soils.  The  method  is  as  fol- 
lows: the  beds  are  thoroughly  prepared  in  the  usual 
way,  and  then  drenched  with  a  gallon  per  square 
foot  of  formaldehyde  solution  composed  of  one  pint 
of  commercial  formaldehyde  (40%  pure)  to  thirty 
gallons  of  water.  The  solution  should  be  put  on  with 
a  watering  can  and  distributed  as  evenly  as  possible 
over  the  bed,  so  as  to  wet  the  soil  thoroughly  to  a 
depth  of  a  foot.  It  will,  in  most  cases,  be  necessary 
to  apply  the  solution  two  or  three  times,  as  the  soil 
may  not  absorb  the  full  quantity  of  the  liquid  at  one 
time.  After  the  treatment  the  beds  should  be  cov- 
ered with  a  heavy  burlap  to  keep  in  the  formaldehyde 
fumes  for  a  day  or  two,  and  then  aired  for  a  week 
before  planting.  Stirring  the  soil  at  once  would  help 
the  escape  of  the  fumes.  Formaldehyde  may  be 
bought  in  any  drug  store  40%  pure. 

Steaming.  This  method  of  treatment  is  far  supe- 
rior to  any  other  yet  evolved.  For  seed  beds  on  a 
large  scale  the  inverted  pan  method  is  the  best.  This 
was  first  devised  by  A.  D.  Shamel  of  the  U.  S.  De- 
partment of  Agriculture.  The  boiler  must  be  able  to 
generate  a  pressure  of  not  less  than  eighty  pounds, 
which  should  be  maintained  for  at  least  one  and  a 
half  hours.  In  setting  a  pan  the  rim  is  sunk  into  the 
soil  of  the  seed  bed,  to  a  depth  of  two  to  three  inches, 
to  make  the  inclosed  chamber  steam  tight.  In 
heavy  soil,  trenching  may  be  necessary.  It  is  also 
advisable  to  put  a  heavy  weight  on  the  pan  when  the 


FIG.  9.     INVERTED  PAN  FOR  STEAM  STERILIZATION.     (AFTER  SELBY.) 


FIG.  10.     SURFACE  WATERING.  SHOWING  PORTABLE  SPRAY  EQUIPMENT 
USED  IN  GARDENS  ABOUT  COLD  FRAMES  AND  HOT  BEDS. 
(AFTER   WILLIAMS.) 


Methods  of  Treating  Sick  Soils        55 

steam  operates.  When  one  pan  is  used,  a  traction 
engine  or  a  portable  boiler  of  ten  to  twelve  H.  P. 
will  suffice.  While  the  standard  size  of  the  pan  is 
six  by  eight  feet,  the  dimensions  may  be  modified 
to  suit  the  size  of  the  seed  beds. 

Selby  and  Humbert1  describe  the  method  of  con- 
structing an  inverted  (fig.  9)  pan  as  follows : 

"Material  used  for  construction  of  a  pan  is  gal- 
vanized sheet  iron;  the  most  useful  weight  is  No.  20 
gauge,  which  weighs  26.5  ounces  per  square  foot. 
The  heavier  material  requires  little  in  the  way  of 
frame  supports.  The  galvanized  iron  sheets  come  in 
sizes  varying  from  two  to  three  feet  in  width  by  eight 
to  ten  feet  in  length.  Figure  9  shows  a  pan  6  x  10 
feet  in  size,  6  inches  deep,  constructed  from  five  such 
strips  2>£  x  8  feet  in  size.  These  sheets  are  joined  by 
double-fold  seam  and  riveted  at  intervals  of  6  to  10 
inches  to  make  the  pan  steam  tight.  This  pan  is 
further  strengthened  by  a  band  of  strap  iron  2x1  inch 
riveted  to  the  bottom  edge,  and  stiffened  by  a  brace 
of  i%  inch  angle  iron  across  the  top  and  extending 
down  the  sides.  This  is  bolted  at  the  sides  to  the 
supporting  strap  iron  stiffener.  The  corner  illustra- 
tions show  at  'A'  the  joint  used  for  the  galvanized 
iron  sheets,  and  'B'  a  section  of  the  angle  iron  sup- 
porting the  top. 

"The  entrance  pipe  for  the  steam  may  be  placed 
at  the  side  or  end  of  the  pan  (see  dotted  construction 
lines  of  fig.  Q)  or  may  enter  from  the  top  as  per  illus- 

1  Selby,  A.  D.,  and  Humbert,  J.  G.,  Ohio  Agr.  Expt.  Sta.  Circ.  151  : 
65-74,  1915. 


56      Diseases  of  Truck  Crops 

tration.  The  latter  form  has  the  advantage  in 
that  it  will  not  interfere  with  the  box  boards  when 
used  on  frames.  The  pipe,  after  entrance,  should 
be  a  T  form,  so  that  steam  in  being  forced  into 
the  pan  when  in  place  does  not  blow  holes  in  the 
soil." 

Surface  Firing.  This  method  of  soil  sterilization  is 
used  only  in  the  absence  of  steam  facilities  or  where 
formaldehyde  cannot  be  obtained,  which,  however, 
is  seldom  the  case.  It  consists  simply  in  producing 
a  hot  fire  for  an  hour  or  more  over  the  bed  to  be  ster- 
ilized. A  combustible  material  such  as  brush,  straw, 
or  wood  may  be  used  for  that  purpose.  The  objec- 
tion to  it  is  that  the  fire  may  destroy  the  organic 
matter  in  the  soil. 

Roasting  or  Pan  Firing.  In  this  method  the  soil 
to  be  sterilized  is  removed  from  the  bed  and  placed 
in  a  pan,  underneath  which  fire  is  present.  After 
roasting  the  soil  is  returned  to  the  bed  and  more 
of  it  sterilized.  This  method  is  too  slow  and  is 
open  to  the  same  objection  as  the  surface  burning. 
The  advantage  of  steam  sterilization  and  of  the 
"fire"  methods  consists  in  the  destruction  of  all 
weed  seed,  together  with  the  fungi  which  cause 
damping  off. 

Other  Methods  of  Control.  Damping  off  may  be 
largely  controlled  by  careful  cultural  conditions. 
Unless  the  soil  of  the  seed  bed  is  to  be  sterilized,  it 
is  never  wise  to  sow  the  seeds  in  beds  where  damping 
off  was  known  to  have  occurred  previously.  Thick 
sowing  especially  should  not  be  permitted.  In 


Methods  of  Treating  Sick  Soils        57 


Table  8,  Johnson1  presents  some  interesting  data  on 
the  effect  of  thick  sowing  on  damping  off. 

y     TABLE  8 
Effect  of  Thick  Sowing  on  Percentage  of  Diseased  Plants. 


Flat  No. 

Weight  of  seed  sown 

Plants  Diseased 

per  flat 

per  JOO  sq.  ft. 

i. 

Grams 

O.I 
0.2 

0-3 
0.4 

0-5 
0.6 
0.7 
0.8 
0.9 

I.O 

Ounces 
0.16 

0.33 
0.49 
0.66 
0.83 
0.99 
1.16 

1-33 
1.49 
i.  60 

Per  cent. 
o 
o 
8 
15 
35 

& 

80 
92 
96 

2 

3~ 

6 

7 

8 

9, 
10  

Certain  soils  are  especially  favorable  to  damping 
off.  Soils  which  contain  a  high  percentage  of  un- 
rotted  vegetable  matter  and  those  which  are  hard  to 
drain  need  especial  attention.  Great  care  should  be 
taken  that  the  seed  bed  is  kept  at  the  right  tempera- 
ture. The  latter  cannot  be  guessed  at  by  personal 
sensation.  It  should  be  accurately  determined  by 
thermometers  placed  in  the  bed  at  suitable  distances. 
It  should  also  be  remembered  that  any  covering  cloth 
or  sash  will  exclude  light  and  air.  Every  precaution 

1  Johnson,  James,  Wisconsin  Agr.  Expt.  Sta.  Research  Bui.  31: 
31-61,  1914. 


58      Diseases  of  Truck  Crops 

should  be  taken  to  prevent  the  seedlings  from  be- 
coming "drawn,"  for  at  that  stage  they  are  most 
susceptible  to  damping  off.  The  safest  plan  is  to 
keep  the  temperature  a  trifle  lower  than  is  gener- 
ally required,  and  allow  as  much  ventilation  as 
possible.  Very  often  damping  off  starts  in  one 
corner  of  the  bed.  To  check  the  rapid  spread  of  the 
disease,  the  infected  area  may  be  removed.  Spray- 
ing the  seedlings  with  various  fungicides  in  a  bed 
where  damping  off  has  become  well  established  will 
be  of  little  help. 

CONTROL  OF  FUSARIUM-  AND  NEMATODE-SICK  SOILS 

The  formaldehyde  or  the  steam  sterilization  meth- 
ods which  are  so  effective  in  the  treatment  of  sick 
seed  beds  cannot  be  used  on  a  large  scale  for  sick 
soils  on  account  of  the  extensive  cost  involved.  The 
trucker,  therefore,  must  resort  to  other  methods  of 
control.  Soils  which  are  made  sick  by  the  presence 
of  parasitic  fungi  or  nematodes  may  be  reclaimed  by 
crop  rotation  as  well  as  by  the  development  of  wilt- 
resistant  varieties.  Both  of  these  methods  will  be 
discussed  at  length  in  pages  372,  373. 

CONTROL  OF  INSECT-INFESTED  SOIL 

Spraying  the  soil  will  be  of  little  value  in  the  control 
of  underground  insect  pests.  Fortunately,  however, 
we  have  more  effective  means  for  dealing  with  them. 
To  destroy  wireworms,  sow  corn  which  has  been 


Methods  of  Treating  Sick  Soils        59 

soaked  for  ten  days  in  water  containing  arsenic 
or  strychnine  sulphate  before  planting  the  regular 
crop.  The  larvae  will  feed  on  the  poisonous  corn 
kernels  and  die.  Another  way  is  to  treat  the  seed 
with  gas  (coal)  tar. 

White  grubs  may  be  controlled  by  the  use  of  bisul- 
phide of  carbon.  Fall  plowing  is  a  valuable  remedy, 
since  many  of  the  grubs  are  thus  exposed  to  the  cold 
winter  weather  and  killed. 

Cutworms  may  be  controlled  by  the  use  of  a 
poisoned  bran  made  as  follows:  to  three  ounces  of 
molasses  add  one  gallon  of  water  and  sufficient  bran 
to  make  a  fairly  stiffened  mixture.  To  this  add  Paris 
green  or  arsenic  and  stir  well  into  a  paste.  A  heap- 
ing teaspoonful  of  the  mixture  is  scattered  here  and 
there  over  the  infested  land. 


PART   II 


61 


CHAPTER  V 

THE  HEALTHY  HOST  AND  ITS  REQUIREMENTS 

WE  have  seen  that  soil  is  the  medium  in  which 
plant  life  is  made  possible.  We  have  also  seen 
that  to  produce  good  yields  in  crops  it  is  essen- 
tial to  have  a  healthy  soil — a  condition  directly 
dependent  upon  the  work  of  friendly  organisms. 
When  these  perform  their  work  imperfectly,  or 
when  the  soil  is  overrun  by  parasitic  fungi  or 
by  pestiferous  animal  life,  the  soil  is  considered 
sick. 

Let  us  now  consider  the  plant  itself,  since 
practically  and  economically  it  is  the  crop 
that  concerns  us  most.  We  are  interested  in 
the  soil  only  in  so  far  as  it  is  capable  of  main- 
taining economic  crops.  The  general  needs  of 
plant  life  are  the  same  to  a  striking  extent  for 
higher  plants  and  for  the  lower  micro6rganisms 
of  the  soil. 

NEED  OF  AIR 

Plants  must   breathe,  since  air  is  indispensable 

63 


64  Diseases  of  Truck  Crops 

for  all  life.  Plants  breathe  through  their  leaves, 
and,  according  to  Whitney, x  through  the  roots  also. 
Hence,  cultivation  is  necessary  not  only  to  supply 
air  to  the  microorganisms  in  the  soil,  but  also  to 
the  roots  of  the  crop.  In  the  opinion  of  Whitney, 
cultivation  accomplishes  a  step  further;  by 
stirring  the  soil  we  permit  the  escape  of  foul  gases 
given  off  by  the  plant  roots  as  well  as  by  the  soil 
organisms. 


NEED  OF  WATER 


Plants  to  live  must  drink.  This  is  one  of 
the  most  important  considerations  from  the 
trucker's  point  of  view.  It  is  generally  sup- 
posed that  roots  are  fixed  things  in  the  soil, 
receiving  water  and  food  material  by  capillary 
action.  This  occurs  only  in  very  moist  and 
saturated  soils.  However,  in  dry  seasons  and 
in  dry  soils  the  roots  have  to  move  down- 
ward towards  the  water.  This  may  be  proved 
by  a  simple  ingenious  experiment  described  by 
Whitney.  "If  you  take  some  soil  from  the 
field  with  what  we  call  an  optimum  amount  of 
moisture,  or  the  best  amount  for  plant  growth, 
put  it  in  a  tumbler,  filling  the  tumbler  about 
half  full,  and  put  some  dry  soil  on  the  surface, 

1  Whitney,  Milton,  U.  S.  Depart,  of  Agr.  Farmers  Bui.  257: 
5-35,  1909- 


Healthy  Host  and  Its  Requirements    65 

you  can  see  the  difference  in  moisture  contents 
by  the  difference  in  color,  the  moist  soil  being 
darker  than  the  dry.  Then,  if  you  cover  the 
tumbler  to  prevent  evaporation  you  can  leave 
the  dry  soil  in  contact  with  the  moist  soil  and 
there  will  be  no  appreciable  interchange  of  mois- 
ture between  the  moist  and  the  dry  layers.  This 
simple  experiment  demonstrates  that  if  cultiva- 
tion is  also  to  conserve  the  soil  moisture,  we 
must  always  strive  to  form  a  pulverized  dry 
mulch  on  top.  Capillary  action  practically  ceases 
when  a  dry  mulch  or  layer  is  found  on  top  of  the 
soil." 

From  the  trucker's  point  of  view,  the  water  re- 
quirement of  crops  deserves  careful  consideration. 
In  intensive  gardening  the  water  supplied  by  natural 
precipitation  of  rainfall  cannot  always  be  depended 
upon  for  crop  production,  and  must  be  supplemented 
by  irrigation.  In  fact  irrigation  is  often  a  funda- 
mental requirement,  if  we  are  to  meet  in  a  timely  way 
the  demands  of  the  market.  Irrigation  when  prop- 
erly carried  out  may  mean  success,  and  the  opposite 
total  failure.  To  be  what  farmers  call  a  "water 
hog,"  using  too  much  water,  is  detrimental  to  the 
crops,  for  they  are  very  sensitive  to  an  excess  of  it. 
Widtsoe  and  Merrill '  have  shown  that  the  yields  of 
truck  crops  directly  depend  on  the  proper  amount  of 
water  supplied.  The  result  of  their  investigation  is 
shown  in  Table  9. 

1  Widtsoe,  J.  A.f  and  Merrill,  L.  A.,  Utah  Agr.  Expt.  Sta.  Bui.  117: 
69-119,  1912. 

51 


66 


Diseases  of  Truck  Crops 


TABLE  9 

The  Yields  of  Truck  Crops  as  Harvested,  with  Different 
Quantities  of  Water 

Yield  of  crops  is  expressed  in  Ibs.  per  acre;  quantities  of  water  used 
are  expressed  in  acre-inches.* 

CARROTS 


i.  Irrigation  water  supplied 
2.  Rainfall  and  soil  water  .  . 
3.  Total  water  for  use  of 
crop  .  .  . 

3-75 
10.25 

14.00 

7.50 
10.25 

I7.7S 

15.00 
10.25 

2S-2S 

25.00 
10.25 

35.25 

35-°° 
10.25 

45.25 

60.00 
10.25 

70.2  <S 

4.  Total    yield    of    carrots 
(Ibs  per  acre) 

^4S77 

3^223 

49SO7 

467  SS 

56930 

68420 

5.  Yield  per  inch  of  irriga- 
tion water.  . 

Q22I 

441O 

3106 

1871 

1627 

1129 

6.  Yield  per  inch  of  total 
water. 

246Q 

1872 

1963 

1326 

1258 

974 

CABBAGE 


I.  Irrigation  water  supplied  
2.  Rainfall  and  soil  water  
3.  Total  water  for  use  of  crop.  .  .  . 
4.  Total  yield  of  cabbage  (Ibs.  per 
acre)  . 

12.50 

5-54 
18.04 

18400 

20.00 
5-54 
25-54 

18524 

25.00 
5-54 
30-54 

16310 

40.00 

5-54 
45-54 

20432 

70.00 

5-54 
75-54 

23098 

5.  Yield    per    inch    of    irrigation 
water. 

1479 

926 

652 

511 

33° 

6.  Yield  per  inch  of  total  water..  . 

1025 

725 

534 

449 

306 

ONIONS 


I    Irrigation  water  supplied.  .  .             ... 

15.00 

20.00 

3O.OO 

65.00 

2   Rainfall  and  soil  water                   .... 

5-54 

5.54 

5.54 

5.54 

3  Total  water  for  use  of  crop  

20.54 

25.54 

35-54 

70.54 

4.  Total  yield  of  onions  (Ibs.  per  acre)..  . 
5.  Yield  per  inch  of  irrigation  water  
6.  Yield  per  inch  of  total  water  

21471 
1432 
1045 

22038 

1  102 

863 

32437 
1098 

913 

34I7I 
526 
484 

1  The  term  acre-inch  means  the  quantity  ttfet  will  cover  one  acre  to 
the  depth  of  one  inch.  Likewise  in  speaking  of  an  acre-foot  of  water, 
it  means  the  water  necessary  to  cover  one  acre  to  a  depth  of  one  foot. 


Healthy  Host  and  Its  Requirements    67 

A  careful  study  of  Table  9  shows  that  excessive 
watering  results  in  a  decrease  of  yield.  Widtsoe  and 
Merrill  in  their  work  on  sugar  beets  found  that  when 
30  acre-inches  of  water  is  spread  over  one  acre  30 
inches  deep,  the  yield  was  20.82  tons.  When  this 
same  amount  of  water  was  spread  over  two  acres 
and  for  a  depth  of  fifteen  inches,  the  yield  increased 
to  38.90  tons  per  acre.  Finally  when  the  30  acre- 
inches  of  water  were  spread  over  six  acres  and  five 
inches  deep,  the  yield  increased  to  82.68  tons  per 
acre.  Every  trucker  should  study  the  water  require- 
ments of  the  crops  under  his  conditions  of  soil  and 
climate.  To  obtain  the  best  results  from  irrigation 
we  must  be  familiar  with  the  root  system  of  each 
particular  crop  and  the  depth  to  which  it  normally 
penetrates  the  ground. 

Methods  of  Irrigation.  There  are  two  methods  of 
watering  recommended.  Each  trucker  can  determine 
for  himself  which  of  the  two  will  give  him  the  best 
results  under  his  particular  conditions. 

(a)  Subirrigation.  As  this  implies,  the  water  is 
applied  underground  and  through  perforated  pipes. 
The  conditions  necessary  for  subirrigation  are  a  clay 
subsoil  or  a  hardpan  capable  of  retaining  the  irriga- 
tion water.  The  topsoil  must  be  of  a  sandy  loam, 
neither  too  loose  nor  too  compact.  The  land  must 
be  of  a  nature  to  admit  of  perfect  drainage,  having 
a  fall  of  one  inch  to  each  one  hundred  feet.  The  land 
must  also  be  level  without  raised  places.  Where 
these  conditions  cannot  be  fulfilled,  subirrigation 
will  prove  a  failure.  The  crops  that  are  best  bene- 


68  Diseases  of  Truck  Crops 

fited  by  subirrigation  are  celery,  lettuce,  and  Irish 
potatoes.  Tomatoes,  watermelons,  cantaloupes,  or 
sweet  potatoes  are  not  benefited  by  it. 

The  advantages  claimed  for  subirrigation  are  many : 
(i)  The  moisture  is  better  controlled  in  the  soil  and 
the  roots  will  have  easy  access  to  it.  (2)  No  crust 
is  formed  to  shut  out  the  air  from  the  soil,  or  to  fa- 
vor the  development  of  fungous  diseases.  (3)  The 
soluble  salts  and  fertilizers  are  not  washed  down 
deeply  and  are  not  carried  beyond  the  reach  of  the 
roots. 

(b}  Surface  or  Spray  Irrigation.  As  this  implies, 
water  is  applied  on  the  surface  overhead,  in  the  form 
of  rain  (fig.  10).  The  many  advantages  claimed  for 
this  system  are  as  follows :  (i)  For  the  same  volume  of 
water  a  much  larger  area  may  be  irrigated,  or  the 
same  area  may  be  watered  with  a  smaller  quantity  of 
water.  (2)  Very  little  skilled  labor  is  necessary  in 
this  system.  (3)  Large  areas  for  irrigation  can  be 
rapidly  covered.  (4)  The  rain  effect  will  control 
frosts.  (5)  There  are  no  leaky  wasteful  channels,  and 
no  boggy  roads.  (6)  An  economy  of  land  in  channels 
and  ditches.  (7)  Spray  irrigation  is  independent 
of  the  topography  of  the  field,  and  may  be  extended 
to  lands  too  rolling  or  rough  for  subirrigation. 
Truckers  in  the  arid  sections  seem  in  favor  of  a  com- 
bination of  spray  and  surface  irrigation  on  the  same 
field.  The  spray  is  used  in  preparing  the  seed  bed, 
germinating  the  seeds,  and  for  newly  set  out  plants. 
Later,  as  the  crop  advances  in  age,  especially  during 
blossoming  and  fruiting,  irrigation  is  carried  out  by 


Healthy  Host  and  Its  Requirements    69 

surface  furrow  or  check  methods.  A  portable 
spray  equipment  meets  these  conditions  well.  The 
disadvantage  of  this  system  like  that  of  rain  is  the 
baking  of  the  surface  soil,  thereby  necessitating  more 
frequent  cultivations.  Moreover,  when  spray  ir- 
rigation is  overdone  it  is  likely  to  encourage  the 
development  of  mildews  and  various  leaf  spots. 

NEED  OF  SANITARY  ENVIRONMENTS 

Science  has  shown  us  the  reasons  for  sanitary  liv- 
ing for  men  and  animals  and  equally  for  plants. 
Since  the  soil  is  the  home  of  the  plant,  we  must  keep 
that  soil  as  clean  as  we  do  our  houses,  or  the  stalls  in 
stables.  The  soil  organisms  give  off  numerous  poison- 
ous excreta,  which  become  harmful  to  them  and  to 
the  crops.  Through  their  own  activities,  the  roots  of 
plants,  too,  throw  off  certain  poisonous  excreta.  If 
they  are  allowed  to  accumulate  in  the  soil  through 
growing  the  same  crop  too  long  in  the  same  soil,  a 
point  is  reached  where  that  crop  will  refuse  to  grow 
there  any  longer,  even  if  there  is  no  evidence  of  soil 
exhaustion.  The  best  purifier  of  soils  is  organic 
matter  applied  as  manure  or  green  vegetable  matter 
which  is  converted  into  humus. 

Clean  Culture.  There  are  two  other  means  by 
which  we  can  keep  soils  in  a  sanitary  condition. 
Rotation  of  crops  is  discussed  on  page  372.  Clean 
culture,  too,  is  an  essential  means  of  safeguarding 
the  health  of  our  economic  plants.  Not  only  do 
weeds  help  to  carry  fungous  diseases  which  are  also 


7O  Diseases  of  Truck  Crops 

common  to  crops,  but  they  too  excrete  certain  poisons 
into  the  soil  which  become  harmful  to  the  crop  in 
the  company  of  which  they  grow.  Moreover,  weeds 
rob  the  soil  of  vast  quantities  of  water  which  other- 
wise would  be  utilized  by  crops.  This  is  an  important 
consideration  where  irrigation  is  not  practiced  ex- 
tensively and  in  the  more  arid  regions. 


CHAPTER  VI 

CAUSES  OF  DISEASES   IN  CROPS 

IT  is,  indeed,  very  difficult  to  define  the  term  dis- 
ease. Health  and  disease  are  only  relative  terms,  and 
it  is  not  easy  to  draw  a  line  where  health  leaves  off 
and  disease  begins.  Disease,  however,  may  be  ap- 
plied to  all  deviation  from  the  normal  which  threatens 
the  life  of  the  plant.  Perhaps  the  nearest  conception 
of  health  and  disease  is  that  of  Marshal  Ward,  who 
says:  "If  we  agree  that  a  living  plant  in  a  state  of 
health  is  not  a  fixed  and  unaltering  thing,  but  is  ever 
varying  and  undergoing  changes  as  its  life  works  out 
its  labyrinthine  course  through  the  vicissitudes  of  the 
ever- vary  ing  environment,  then  we  cannot  escape  the 
conviction  that  a  diseased  plant,  so  long  as  it  lives, 
is  also  varying  in  response  to  the  environment.  The 
principal  difference  between  the  cases  is,  that  whereas 
the  normal  healthy  plant  varies  more  or  less  regu- 
larly and  rhythmically  about  a  mean,  the  diseased 
one  is  tending  to  vary  too  suddenly  or  too  far 
in  some  particular  direction  from  the  mean.  The 
healthy  plant  may,  for  our  present  purposes,  be 
roughly  likened  to  a  properly  balanced  top  spinning 
regularly  and  well,  whereas  the  diseased  one  is  lurch- 

71 


72  Diseases  of  Truck  Crops 

ing  here,  or  wobbling  there,  to  the  great  danger  of  its 
stability.  For  we  must  recognize  at  the  outset  that 
disease  is  but  variation  in  directions  dangerous  to  the 
life  of  the  plants.  That  the  passage  from  health  to 
disease  is  gradual  and  ill-defined  in  many  cases 
will  be  readily  seen."  Excluding  the  injury  from 
insect  pests,  the  diseases  of  truck  crops  may  be  con- 
sidered as  follows: 

A.    DISEASES  OF  A  MECHANICAL  NATURE 

Diseases  brought  about  by  mechanical  injuries  are 
very  numerous  and  varied.  Truck  crops  such  as 
spinach,  lettuce,  etc.,  are  cultivated  for  their  edible 
tender  parts.  It  is  not  strange  that  such  crops  should 
be  susceptible  to  injuries  of  a  mechanical  nature. 

WIND  STORMS 

Wind  storms  are  often  the  cause  of  great  losses  to 
the  trucker.  This  is  especially  the  case  in  soil  dis- 
tricts of  a  sandy  nature.  Strong  winds  cause  the 
sand  to  be  thrown  about  in  the  field  with  consider- 
able force  and  velocity.  The  small  sand  particles 
blown  violently  on  plants  cut  the  foliage  and  not 
infrequently  the  fruit  too.  Tomatoes,  watermelons, 
eggplants,  in  fact,  all  the  tender  crops,  suffer  greatly 
from  sand  or  dust  storms.  Besides  this  form  of 
injury,  dust  or  sand  storms  carry  off  large  quantities 
of  fertilizer.  Moreover,  sick  particles  of  soils  may 
be  carried  by  the  wind  from  farm  to  farm,  and  in  this 


Causes  of  Diseases  in  Crops         73 

way  soil  diseases  be  spread.  Wind  storms  cannot 
well  be  prevented.  Perhaps  the  best  safeguard  is 
never  to  allow  bare  spaces  in  the  field,  and  to  have 
the  soil  thoroughly  covered  with  vegetation.  In 
windy  localities,  crops  should  be  planted  closer  than 
is  generally  the  custom. 

RAINSTORMS 

Heavy  rains  when  pounding  on  tender  plants  may 
cause  considerable  damage  in  tearing  tender  foliage. 
Another  indirect  injury  is  the  pounding  and  packing 
of  the  soil.  This  shuts  out  the  free  circulation  of  air 
and  is  bound  to  interfere  with  the  normal  metab- 
olism of  the  plant.  Heavy  rains  by  pounding  on  the 
soil,  splash  mud  and  sand  on  all  parts  of  the  plant. 
This  encourages  infection  of  numerous  diseases,  and 
reduces  the  shipping  and  market  value  of  the  crop. 

Besides  rainstorms,  frequent  showers  are  detri- 
mental to  truck  crops  cultivated  for  their  fruit  or 
seed.  They  prevent  pollination  by  insects.  There 
is,  of  course,  no  feasible  method  of  preventing  un- 
favorable weather  conditions.  Deep  plowing  may 
encourage  the  absorption  of  all  the  rain  and  prevent 
baking.  Windbreaks  too  may  protect  crops  from 
severe  storms. 

HAILSTORMS 

The  injury  to  truck  crops  from  this  source  is  con- 
siderable. It  results  in  deep  bruises  or  cuts  in  stem, 


74  Diseases  of  Truck  Crops 

foliage,  and  fruit.  The  writer  knows  of  cases  where 
large  areas  of  tomatoes,  cantaloupes,  and  waterm  jlons 
were  totally  ruined  by  hail.  With  the  sweet  potato 
hail  does  not  always  ruin  the  crop,  but  it  retards  it. 
The  foliage  and  vines  dry  up  as  a  result  of  the  me- 
chanical cutting  and  bruising  from  hail,  but  new 
growth  soon  follows.  Even  when  hail  does  not  ruin 
a  crop,  there  is  danger  of  infection  at  the  place  of 
each  cut  or  bruise  (fig.  n).  If  the  affected  crop 
is  valuable  and  shows  promise  of  recovery,  it  should 
be  sprayed  with  a  good  standard  fungicide. 

LIGHTNING  INJURY 

Injuries  to  trees  from  lightning  are  familiar  to 
all.  Jones  and  Gilbert1  record  an  interesting  case 
of  lightning  injury  to  potato  plants.  The  injury  is 
noticed  in  round  spots  in  the  field  (fig.  12  a),  the 
spots  varying  from  ten  to  twenty  feet  in  diameter. 
The  potato  tops  appear  broken  and  disheveled 
and  upon  drying  off,  within  twenty -four  hours 
they  wilt  and  die.  In  examining  the  individual 
plant  we  find  that  the  stem  collapses  and  the  top 
falls  over,  the  stem  browns  and  shrivels  faster  above, 
and  less  rapidly  below  this  point.  The  pith  at  this 
region  browns  and  collapses,  leaving  a  hollow  stem, 
but  without  any  softening  such  as  usually  occurs 
with  blackleg.  No  evidence  of  splitting  or  mechan- 
ical rupture  of  the  stem  has  been  observed.  Light- 
ning injury  may  occur  when  thunderstorms  are  very 

1  Jones,  L.  R.,  and  Gilbert,  W.  W.,  Phytopath.    5  :  94-101,  1915. 


\ 


FIG.  ii.  WATERMELON  SLICE  SHOWING  HAIL  INJURY.  ARROWS  IN- 
DICATE PLACE  OF  INJURY  FOLLOWED  BY  A  ROTTING  DUE  TO  THE 
SECONDARY  INVASION  OF  SEMI-PARASITIC  FUNGI. 


Causes  of  Diseases  in  Crops          75 

prevalent,  usually  during  July.  It  may  be  found  in 
sandy  as  well  as  clay  loam  fields,  and  the  contour  of 
the  land  seems  to  have  no  influencing  effect.  The 
following  is  Jones  and  Gilbert's  explanation  of  the 
phenomenon:  "When  an  electric  storm  breaks  sud- 
denly following  a  period  of  dry  weather  and  the  first 
rain  wets  the  topsoil,  there  remains  a  layer  of  dry 
earth  between  this  wet  surface  and  the  moist  soil 
underneath,  which  is  a  poor  conductor  of  electricity. 
When  the  lightning  strikes  the  wet  surface  spot,  it 
disperses  in  all  directions,  horizontally  and  then 
downwards  into  the  earth,  following  lines  of  least 
resistance.  The  plant  stems  and  roots  with  their 
abundant  water  content  are  better  conductors  than 
the  layer  of  dry  soil  just  mentioned,  and  so  the 
electric  current  passes  through  them.  The  tissues 
may  thus  be  variously  injured  or  killed,  depending 
upon  the  amount  of  current  passing  through  them. " 

FROST  INJURY 

The  greatest  profits  in  trucking  are  generally  made 
when  crops  are  available  for  the  early  market. 
This  means  that  truckers  must  be  prepared  to  meet 
losses  directly  due  to  spells  of  frost.  Not  all 
truck  crops  are  equally  sensitive  to  frost,  but  we 
have  as  yet  no  crops  which  are  absolutely  frost 
proof.  When  the  temperature  at  which  condensa- 
tion of  moisture  in  the  air  takes  place  is  below  freez- 
ing, ice  may  form  in  the  intercellular  spaces,  and 
the  plant  is  then  destroyed,  without  any  frost 


76  Diseases  of  Truck  Crops 

deposited  on  the  outside.  Equal  injury  results 
when  the  exterior  of  the  plant  is  at  or  below  the 
freezing  point,  and  frost  is  deposited  on  the  plant. 
It  is  supposed  that  in  this  case  the  cold  does  not 
freeze  the  water  in  the  cells,  but  draws  it  out.  The 
more  sap  a  plant  has,  the  faster  it  is  withdrawn. 
In  this  case,  then,  the  plant  dies  not  from  cold 
but  from  drought. 

Frost  conditions  are  determined  by  various  fac- 
tors. Trucking  lands  situated  near  large  bodies  of 
water  generally  enjoy  immunity  from  frost  not  found 
in  inland  localities.  Tender  crops  growing  on  low 
hills  or  on  greatly  sloping  hillsides,  somewhat  above 
the  valley  floor,  are  also  well  protected  from  frost. 
Lowlands,  particularly  those  which  have  no  outlet 
through  which  the  cold  air  may  drain  off,  are  not 
suited  for  early  trucking  because  of  the  danger  from 
frost.  Lands  which  are  properly  drained  and  cul- 
tivated will  not  only  produce  larger  yields,  but  will 
also  be  protected  from  frost. 

How  to  Predict  Frost.  There  are  usually  several 
signs  which  the  trucker  may  use  as  a  warning  of  the 
approach  of  frost.  Frost  should  be  looked  for  after 
unusual  warm  spells  in  the  spring.  The  state  of  the 
sky  is  also  an  indication.  Frost  is  not  likely  to  occur 
when  the  sky  is  overcast  because  the  heat  given  off 
by  the  earth  at  night  does  not  easily  penetrate  the 
clouds  and  is  therefore  retained  in  the  air  below. 
On  the  other  hand,  during  clear  nights,  the  earth's 
heat  readily  escapes  and  this  is  likely  to  result  in  a 
disastrous  drop  of  temperature.  Frost  is  brought 


Causes  of  Diseases  in  Crops          77 

about  also  by  a  sudden  change  from  wind  to  calmness 
of  air.  Winds  prevent  frost  formation  because  they 
prevent  the  accumulation  of  the  colder  air  at  the 
surface.  The  trend  of  temperature  is  also  an  im- 
portant consideration.  A  temperature  of  forty 
degrees  at  about  6  p.  M.  with  a  clear  sky  may 
indicate  the  approach  of  frost.  A  fall  of  tempera- 
ture of  two  degrees  an  hour  in  the  afternoon  would 
also  indicate  the  approach  of  frost.  If  the  air  pres- 
sure is  increasing  rapidly,  as  indicated  by  a  rapid 
rise  in  the  barometer,  frost  may  be  approaching.  A 
change  in  pressure  usually  precedes,  by  a  short  in- 
terval, the  change  in  direction  of  wind. 

How  to  Protect  Crops  from  Frost.  Crops  may 
be  protected  from  frost  in  two  ways,  (i)  Arti- 
ficial covering  is  an  old  practice  widely  used  by 
truckers,  and  consists  in  protecting  the  plants  by 
covering  them  with  newspapers,  carpets,  sacks,  straw, 
tar  paper,  or  a  mulch  of  soil.  This,  however,  is 
applicable  only  to  small  gardens  or  to  seed  beds. 
On  a  large  scale  it  is  not  practical  because  of  the 
labor  involved.  (2)  Smudging  and  heating  consists 
in  the  burning  of  any  combustible  material  capable 
of  producing  heavy  smoke,  such  as  moist  straw  or 
coal  tar.  Through  smudging  we  prevent  the  escape 
of  the  earth's  heat. 

A  better  method  consists  in  heating  the  air  of  the 
field  by  means  of  evenly  distributed  small  fires  gen- 
erally supplied  by  ovens  of  various  designs.  The 
material  used  is  wood,  coal,  or  oil,  the  choice  being 
determined  by  the  local  price  and  supply.  With 


78  Diseases  of  Truck  Crops 

the  warning  from  an  alarm  thermometer  which  rings 
a  bell  as  the  danger  point  in  temperature  is  reached, 
the  fires  may  be  started.  Smudging  and  heating  are 
extensively  used  by  orchardists.  Truckers,  however, 
have  generally  been  slow  to  adopt  this  method. 

DROUGHT  INJURY 

By  drought  is  meant  a  scarcity  of  water  in  the  soil, 
affecting  and  preventing  the  normal  life  process  of 
plants.  Drought  injury  is  variously  indicated  by 
different  crops.  With  beans,  for  instance,  the  leaves 
lose  their  chlorophyll,  and  the  entire  plant  becomes 
whitish,  brittle,  dead,  and  dry.  With  cabbage,  on  the 
other  hand,  the  tips  of  the  lower  leaves  first  bleach, 
then  wilt,  eventually  drying  and  falling  off.  With 
sweet  corn  the  plants  shrivel  and  bend  over  (fig. 
12  b).  The  amount  of  injury  from  drought  is  pro- 
portional to  the  scarcity  of  the  water  in  the  soil. 
The  only  remedy  for  drought  is,  of  course,  irrigation. 
This  is  especially  true  for  arid  and  semi-arid  regions. 
Trucking  is  never  safe  unless  provisions  are  made 
for  proper  irrigation. 

SMOKE  INJURY 

As  a  rule,  trucking  centers  are  situated  near  large 
cities,  which  are  usually  centers  for  industrial  pro- 
duction and  manufacture.  Truckers  who  are  situ- 
ated nearest  to  manufacturing  plants  are  apt  to  lose 
in  crops  from  the  effect  of  smoke  and  deleterious  gases 
that  escape  from  the  furnaces  into  the  air. 


FIG.  12. 

a.   Lightning  injury,   showing  killed  spot   in  potato   field,   b. 
drought  injury  of  sweet  corn  (a.  after  Jones  and  Gilbert). 


Causes  of  Diseases  in  Crops          79 

The  sources  of  smoke  may  be  classified  into 
three  divisions:  (i)  Smoke  from  large  buildings  or 
from  manufacturing  plants.  (2)  Smoke  from  loco- 
motives. (3)  Smoke  from  chimneys  of  dwelling- 
houses.  Smoke  is  generally  produced  because  of 
improper  furnace  construction,  improper  draft, 
overloaded  boiler,  insufficient  air  space,  insufficient 
air  supply  to  boiler  room,  and  finally  carelessness  of 
operation. 

Smoke  contains  large  quantities  of  carbon  dioxide, 
steam,  and  sulphur  dioxide,  besides  its  characteristic 
soot.  The  latter  consists  of  carbon,  tar,  and  mineral 
matter  mixed  with  small  quantities  of  sulphur, 
arsenic,  and  nitrogen  compounds  which  are  of  an 
acid  nature.  Soot  adheres  to  plants,  especially  to 
foliage,  giving  these  a  burned,  contorted  appearance. 
Another  effect  of  soot  and  smoke  is  to  close  up  the 
stomata  or  respiratory  openings  of  the  leaf,  which 
results  in  asphyxiation.  The  effect  of  smoke  on 
plants  is  loss  of  leaflets  in  case  of  compound  leaves, 
and  abnormal  vegetation  because  of  curling  and 
distortion.  Lesions  and  spots  may  be  formed  on  the 
foliage  as  a  result  of  the  sulphur  dioxide  which  is 
present  in  smoke.  The  spots  are  at  first  small,  but 
soon  enlarge  and  finally  involve  the  whole  leaf,  which 
dries  and  becomes  gray.  Smoke  injury,  although  of 
a  mechanical  nature,  may  also  be  considered  from 
a  physiological  point  of  view.  The  after  effect  of 
smoke  on  plants  resolves  itself  into  a  question  of  in- 
sufficient food  supply  and  assimilation.  This  is 
indirectly  brought  about  by  diminished  illumination, 


8o  Diseases  of  Truck  Crops 

interference  with  the  normal  transpiration,  and  the 
reduction  of  leaf  surface. 

It  seems  that  not  all  truck  crops  are  equally  sub- 
ject to  smoke  injury.  Potatoes  seem  to  be  very  sen- 
sitive to  its  effect,  while  peas  are  the  most  resistant. 

Methods  of  Control.  There  is  as  yet  no  definite 
method  of  control  known.  All  that  the  trucker  can 
do  is  to  avoid  the  smoke  belts.  The  greatest  in- 
jury occurs  in  the  line  of  the  general  direction  of  the 
winds.  These  areas  therefore  should  be  avoided. 
As  far  as  possible,  irrigation  should  be  postponed 
during  windy  days.  The  injury  from  the  smoke  is 
greatest  when  the  soil  is  wet.  Truckers  have  a 
right  to  expect  reimbursement  in  case  of  loss  from 
smoke  injury,  when  the  offending  factory  is  set  up 
subsequent  to  the  trucker's  settlement  in  that  place. 

B.    DISEASES  DUE  TO  PHYSIOLOGICAL  CAUSES 

In  this  class  are  included  disturbances  which  are 
due  to  unfavorable  conditions  of  nutrition.  There 
are  numerous  diseases  of  plants  which  are  brought 
about  by  lack  of,  or  by  an  excess  of,  certain  food 
elements  in  the  soil.  The  effect  is  an  interference 
with  the  proper  life  functions  of  plants. 

MALNUTRITION 

Caused  by  improper  food  supply. 
Symptoms.      The  symptoms  of  malnutrition  are 
not  always  the  same.     They  differ  somewhat  with 


FIG.  13.  MALNUTRITION,  SHOWING  A 
CABBAGE  LEAF  AFFECTED  BY  THE 
DISEASE.  (AFTER  HARTER.) 


Causes  of  Diseases  in  Crops          81 

the  crop,  the  nature  of  the  soil,  and  the  fertilizer 
applied.  In  malnutrition  the  symptoms  to  be 
looked  for  are  retarded  growth,  change  of  color  in  the 
foliage,  and  root  injury.  Affected  plants  remain 
dwarfed  at  a  time  when  maximum  growth  is  expected. 
The  color  of  the  foliage  turns  lighter  green,  especially 
in  the  spaces  between  the  veins  (fig.  13)  which  be- 
come yellowish  green  to  brown.  Roots  of  such 
plants  are  poorly  developed,  and  secondary  roots  or 
rootlets  are  often  missing. 

Causes  of  Malnutrition.  The  work  of  Stone1  and 
Harter2  and  others  seems  to  have  established  the 
fact  that  malnutrition  cannot  be  attributed  to  the 
work  of  parasitic  organisms.  Stone  cites  instances 
where  constant  watering  with  liquid  fertilizers  or 
manure  would  cause  malnutrition  in  cucumber  plants. 
The  same  is  also  induced  when  pig  and  cow  manure 
are  mixed,  or  when  manure  is  worked  into  a  soil 
already  well  fertilized  otherwise.  Harter  records 
cases  of  malnutrition  brought  about  by  an  excess  of 
acidity  in  the  soil.  In  cabbage  fields  suffering  from 
malnutrition,  it  often  required  from  3500  to  6000 
pounds  of  lime  to  neutralize  the  excess  of  the  soil 
acidity.  This  condition  is  apparently  the  result  of 
intensive  trucking  and  the  heavy  applications  of 
chemical  fertilizers  which  leave  the  soil  acid.  Sul- 
phate of  ammonia,  muriate  and  sulphate  of  potash, 

1  Stone,  G.  E.,  Massachusetts  Agr.  Expt.  Sta.,  Ann.  Rept.,  5-13, 
1910. 

2  Harter,  L.  L.,  Virginia  Truck  Expt.  Sta.  Bui.  I   :  4-16,  1909 
(Norfolk,  Va.). 

6 


82  Diseases  of  Truck  Crops 

and  acid  phosphate  when  used  continuously  will 
leave  the  soil  in  a  very  acid  condition.  On  the  other 
hand,  nitrate  of  soda,  carbonate  of  potash,  and 
Thomas  phosphate  tend  to  make  the  soil  alkaline. 

Another  important  cause  of  malnutrition  is  the 
exhaustion  of  humus.  This  is  a  natural  result  where 
commercial  fertilizers  are  used  at  the  expense  of 
any  form  of  organic  manure. 

Methods  of  Controlling  Malnutrition.  From  what 
has  already  been  said,  the  trucker  is  the  loser  if  he 
uses  his  fertilizer  injudiciously.  Not  only  is  malnu- 
trition favored  by  such  a  course,  but  the  yields,  too, 
are  considerably  reduced.  For  instance,  with  cab- 
bage, larger  yields  are  obtained  when  1000  pounds 
of  commercial  fertilizers  are  used  than  from  any 
higher  application.  Liming  to  neutralize  the  soil 
acidity  will  help  control  malnutrition.  To  overcome 
the  humus  deficiency  of  a  soil  the  application  of 
stable  or  green  manure  is  recommended.  The 
amount  of  manure  to  use  will  vary  with  the  crop. 
The  important  thing  to  guard  against  is  the  exces- 
sive use  of  organic  matter.  For  green  manure, 
the  iron  cowpea  is  recommended.  This  variety  is 
resistant  to  wilt,  and  fairly  so  to  root  knot.  The 
best  time  to  plow  under  green  manure  is  generally 
in  October  when  the  plants  approach  maturity. 

BLOSSOM   DROP 

This  is  another  trouble  which  may  be  termed 
physiological,  and  the  cause  of  which  cannot  be 


FIG.  14.  BLOSSOM  DROP,  SHOWING  TO  THE  LEFT  A 
NORMAL  BUNCH  OF  TOMATO  BLOSSOMS  AND  FRUIT,  TO 
THE  RIGHT  MOST  OF  THE  BLOSSOMS  AND  FRUIT  FALLEN 
OFF. 


Causes  of  Diseases  in  Crops         83 

attributed  to  the  work  of  parasitic  organisms.  It 
is  often  noticed  on  tomatoes  (fig.  14)  and  beans. 
Various  causes  may  lead  to  it.  A  period  of  warm 
weather  accompanied  by  cool  nights,  or  by  sudden 
drops  of  temperature,  will  induce  many  truck  crops 
to  shed  their  blossoms.  In  this  case  truckers  are 
helpless,  for  weather  conditions  are  not  controllable. 
Blossom  drop  may  also  be  brought  about  when  too 
much  nitrogen  is  applied  to  the  soil  in  the  form  of 
manure,  hen  manure  especially.  To  overcome  this, 
the  fertilizer  in  the  soil  must  be  balanced  by  the 
addition  of  600  pounds  of  acid  phosphate  and  150 
pounds  of  muriate  of  potash  per  acre. 

C.    DISEASES  OF  UNKNOWN  ORIGIN 
MOSAIC 

This  trouble  extends  practically  to  all  parts  of  the 
host  except  the  roots.  To  the  tomato  grower  the  dis- 
ease is  very  important,  for  it  may  reduce  the  yield 
of  his  crop  by  50  per  cent. 

Symptoms.  Mosaic  is  readily  distinguishable  by 
a  yellow  dotting  or  mottling  of  the  leaf,  presenting 
in  some  instances  a  beautiful  mosaic  structure  (fig. 
15),  whence  its  name.  Affected  leaves  linger  for  a 
time,  but  they  eventually  lose  all  of  their  chlorophyll. 
Another  symptom  is  a  curling  of  the  leaves  resembling 
the  curling  induced  by  green  aphids,  but  in  this 
case  the  insects  have  no  association  with  it.  The 
disease  makes  its  appearance  after  the  seedlings  are 


84  Diseases  of  Truck  Crops 

from  two  to  three  weeks  old,  but  more  often  when  the 
plants  have  attained  full  growth.  Often  the  trouble 
is  so  serious  and  the  curling  so  pronounced  that  the 
plants  thus  affected  cannot  make  any  headway  and 
remain  dwarfed.  An  attempt  is  made  by  the  curled 
plants  to  produce  blossoms,  but  the  latter,  too,  are 
distorted  and  abnormal.  Frequently,  however,  the 
affected  plants  outgrow  the  disease  entirely,  and  thus 
a  distinct  line  of  demarcation  is  observed  between  the 
previously  diseased  part  and  the  healthy  part  of  the 
new  growth.  In  rare  cases,  affected  plants  seem  to 
thrive  in  spite  of  the  disease.  Such  plants  should  be 
selected  for  the  purpose  of  breeding  resistant  strains. 
Cause  of  Mosaic.  The  recent  works  of  Allard1 
and  Freiberg2  have  shown  that  the  cause  of  mosaic 
is  as  yet  a  disputed  question.  Allard  claims  that 
mosaic  is  caused  by  an  ultra-microscopic  pathogen, 
that  is,  a  parasitic  organism  which  cannot  be  de- 
tected by  our  present  technique  in  microscopy. 
Freiberg  claims  that  the  cause  of  mosaic  is  physio- 
logical. The  following  is  a  summary  of  the  claims 
advanced  by  these  two  investigators. 

Allard  Freiberg 

i.     The  virus  is  not  inhibited          I.     The  virus  is  not  inhibitel 
by  concentrations  of  one  part  of      by  formaldehyde, 
formaldehyde  in  100,  200,  400, 
600,  800,  1000,  1200,  and  1500 
parts  of  virus  solution. 

1  Allard,  H.  A.,  "Some  properties  of  the  virus  of  the  mosaic 
disease  of  tobacco,"  Jour.  Agr.  Research,  6  :  649-674,  1916. 

3 Freiberg,  G.  W.,  "Studies  in  the  mosaic  diseases  of  plants," 
Ann.  Missouri  Bot.  Card.,  4  :  I75-232, 


FIG.  15.     MOSAIC,  SHOWING  AFFECTED  PEA  LEAF 


^  *• 

r 


FIG.  16.  BEAN  SEEDS  AFFECTED 
WITH  ANTHRACNOSE,  Colletotri- 
chum  lindemuthianum. 


Causes  of  Diseases  in  Crops 


2.  The  virus  is  not  inhibited  2.  Treatment  with  either 
by  either  chloroform,  carbon  chloroform,  carbon  tetrachloride, 
tetrachloride,  toluene,  or  ace-  toluene,  acetone  or  glycerine 
tone.  do  not  destroy  the  infectious 

properties. 

2a.  The  infectious  properties 
are  destroyed  by  concentrations 
of  alcohol  which  are  destructive 
to  enzymes. 

3.  The    temperatures    which 
destroy  the  infectious  portions 
are  the  same  as  those  which  affect 
enzymes  or  hydrolyze  some  or- 
ganic compounds. 

4.  Cooling  has  no  more  effect 
on  the  infectious  properties  than 
is  exerted  on  any  chemical  com- 
pound, enzyme  included. 

5.  Properties  of  the  infective 
principle  substantiate  the  view 
that  the  infectious  substance  is 
an    enzyme    and    not    a    virus. 
This  enzyme  is  not  of  the  nature 
of  the  oxidases  giving  the  guaia- 
cum  reaction. 

6.  The  reproduction  of  the 
mosaic  enzyme  can  be  accounted 
for    on    purely    physiological 
grounds,  but  the  factors  which 
originally  induced  its  formation 
are    still    unknown.     The    con- 
tinued production  of  the  mosaic 
enzyme  in  inoculated  plants  is 
in  accord  with  the  fundamental 
principles    of    pathology    and 
physiology. 

Work  of  the  future  will  no  doubt  establish  the  true 
cause  of  mosaic. 


3.  The  virus  is  quickly  killed 
at  temperatures  near  the  boiling 
point. 


4.  The  virus  is  highly  resis- 
tant   to   low   temperatures    at 
minus  180°  C.  with  liquid  air  and 
its  infectious  properties  were  not 
weakened. 

5.  The   cause   of   mosaic   is 
not  an  enzyme. 


6.  The  virus  is  a  specific 
particulate  substance  which  is 
not  found  in  healthy  plants. 
Since  this  virus  is  highly  infec- 
tious and  is  capable  of  increasing 
indefinitely  within  susceptible 
plants,  there  is  every  reason  to 
believe  that  it  is  an  ultra  micro- 
scopic parasite  of  some  kind. 


86  Diseases  of  Truck  Crops 

Mode  of  Infection  and  Period  of  Incubation.  Mosaic 
may  be  readily  transmitted  from  plant  to  plant. 
The  easiest  way  to  prove  this  is  to  rub  with  the  rin- 
gers a  diseased  plant,  and  then  immediately  rub  a 
healthy  plant.  The  disease  will  appear  on  the  in- 
oculated host  in  about  ten  days.  In  the  field,  insects 
act  as  carriers  of  mosaic.  The  trucker  may  prevent 
much  of  this  trouble  by  proper  spraying  against  suck- 
ing and  biting  insects. 

D.     DISEASES   DUE  TO  PARASITIC  BACTERIA  OR 

FUNGI 

We  have  already  seen  that  certain  classes  of 
beneficial  bacteria  perform  an  important  function 
in  the  soil.  This,  too,  must  be  true  for  certain 
soil  fungi.  Not  all  microorganisms,  however,  are 
beneficial.  But,  fortunately  for  the  trucker,  only  a 
small  per  cent,  of  bacteria  and  fungi  are  parasitic, 
and  produce  disease  on  plants.  On  page  4  a 
description  was  given  of  the  nature  and  structure  of 
bacteria.  Before  proceeding  further  it  becomes 
necessary  to  familiarize  ourselves  with  the  nature 
of  fungi. 

Fungi.  As  already  stated,  these  are  low  forms  of 
plant  life,  some  of  which  are  beneficial,  while  others 
live  as  parasites  on  the  higher  green  plants,  the  results 
of  which  may  be  considered  as  follows : 

I.  Actual  death  may  result  from  the  destruction 
of  vital  organs  or  tissues.  2.  A  crippling  and  dwarf- 
ing of  plants  due  to  the  slow  destruction  of  the  root 


Causes  of  Diseases  in  Crops          87 

system.     3.     Destruction  of  leaf,  flower,  and  fruit 
without  disturbing  the  root  system. 

FACTORS    WHICH     FAVOR    THE     SPREAD   OF    FUNGOUS 
DISEASES 

The  amount  of  soil  moisture  may  either  protect 
or  predispose  a  certain  crop  to  fungous  disease. 
For  instance,  in  dry  seasons  and  with  a  limited  rain- 
fall, truckers  lose  heavily  from  asparagus  rust 
(Puccinia  asparagi).  In  this  case,  the  lack  of  soil 
moisture  weakens  the  plants,  making  them  therefore 
more  susceptible  to  rust.  An  excess  of  water,  such  as 
is  found  in  poorly  drained  soils,  undoubtedly  favors 
the  spread  of  damping  off,  and  the  numerous 
root  rots.  Weather  conditions  exert  a  powerful 
influence  on  the  prevalence  or  absence  of  plant 
diseases.  Wet  weather  favors  the  spread  of 
downy  mildews  (Peronosporaceae).  Late  blight 
of  potatoes  (Phytophthora  infestans),  downy  mil- 
dew of  lima  beans  (Phytophthora  phaseoli),  and 
many  other  similar  diseases,  are  really  wet  weather 
troubles. 

HOW  PARASITIC  ORGANISMS  ARE  DISSEMINATED 

Fungi  may  be  carried  from  place  to  place  as  bits  of 
mycelium,  as  spores,  or  as  sclerotia.  Fungi  produce 
enormous  numbers  of  spores,  not  all  of  which  find 
their  way  to  receptive  healthy  plants.  Large  num- 
bers are  destroyed  by  exposure  to  sunlight  and  air, 
others  fall  on  crops  upon  which  they  are  unable  to 


88      Diseases  of  Truck  Crops 

thrive,  while  a  relatively  small  proportion  find  ideal 
conditions  on  the  proper  hosts. 

Wind.  If  we  consider  the  microscopic  minuteness 
of  fungous  spores  we  shall  appreciate  how  easy  it  is  for 
winds  and  air  currents  to  become  carriers  of  these 
spores. 

Water.  Water  is  another  important  agent  which 
helps  in  carrying  and  disseminating  fungous  spores. 
The  latter  may  be  actually  carried  in  streams  from  one 
territory  to  another,  or  by  rain  washing  and  splashing 
from  plant  to  plant.  The  spores  of  Phytophthora  in- 
festans,  for  instance,  the  cause  of  late  blight  of  Irish 
potatoes,  are  spread  about  from  plant  to  plant  by  rain. 

Seed-Borne  Diseases.  A  large  number  of  our  truck 
crop  diseases  are  introduced  with  the  seed.  This 
is  often  brought  about  unconsciously  or  through 
carelessness.  Seeds  and  tubers  may  carry  fungous 
pests  as  bits  of  mycelium  in  the  interior  tissue.  An 
example  of  this  is  the  bean  anthracnose  (Colleto- 
trichum  lindemuthianum)  (fig.  16),  which  is  carried 
as  mycelium  within  the  seed.  The  late  blight  of  the 
Irish  potato  is  carried  in  a  similar  way  within  the  tub- 
ers. Seeds  and  tubers  may  also  carry  fungous  pests 
as  spores  or  sclerotia  which  adhere  to  the  exterior  of 
the  seed  coat.  The  smut  of  onions,  for  instance,  is 
carried  as  spores  on  the  onion  seed.  The  Rhizoctonia 
disease  of  Irish  potatoes  is  carried  as  sclerotia  on  the 
surface  of  the  tuber.  The  same  is  true  for  numerous 
other  diseases.  The  methods  of  prevention  of  seed- 
borne  diseases  is  taken  up  on  page  99. 

Insects.     Little  do  we  realize  as  yet  the  importance 


Causes  of  Diseases  in  Crops         89 

of  insects  as  carriers  and  disseminators  of  plant  dis- 
eases. We  are  becoming  increasingly  aware  of  the 
r61e  which  insects  play  in  the  carrying  and  dissem- 
inating of  human  and  animal  diseases.  They  are 
equally  responsible  in  distributing  plant  diseases, 
acting  as  carriers  of  spores  of  parasitic  fungi  which 
may  adhere  to  any  part  of  their  body.  Insects  both 
by  feeding  on  plants  or  in  searching  for  the  nectar  of 
the  blossoms  are  Hkely  to  come  in  contact  with  dis- 
eased parts  of  plants.  In  this  way  their  bodies  may 
become  coated  with  parasitic  bacteria  or  spores  of 
fungi,  which  are  thus  carried  from  plant  to  plant  and 
from  field  to  field.  The  striped  cucumber  beetle, 
for  instance,  is  known  to  carry  and  to  spread  about 
the  virus  of  cucumber  mosaic,  and  the  germ  of 
cucumber  wilt  (Bacillus  tracheiphilus) .  Likewise,  the 
Colorado  potato  beetle  is  a  carrier  of  the  germ  of  the 
Southern  blight  (Bacillus  solanacearum)  of  tomato 
and  potato.  Noxious  insects  act  not  only  as  direct 
carriers  of  spores  of  parasitic  fungi  and  bacteria,  but 
also  induce  diseases  through  the  bites  and  wounds 
which  they  inflict  on  plants  when  feeding.  It  is  there- 
fore very  essential  that  every  effort  which  aims  at  con- 
trolling fungous  pests  should  also  take  in  consideration 
the  control  of  noxious  insects ;  see  page  367. 

E.    DISEASES  INDUCED  BY  PARASITIC  FLOWERING 

PLANTS 

Fungi  and  bacteria,  as  we  have  seen,  are  low  forms 
of  plant  life.     These  derive  their  food  either  from 


90  Diseases  of  Truck  Crops 

living  green  plants  and  are  termed  parasites,  or  from 
dead  organic  matter  and  are  referred  to  as  sapro- 
phytes. Some  higher  flowering  plants,  too,  have  lost 
the  power  of  manufacturing  their  own  food,  and  have 
degenerated  to  the  extent  of  assuming  a  parasitic 
life.  Of  those  which  concern  the  trucker  may  be 
mentioned  the  dodder. 

DODDER    (CuSCUta  Sp.) 

Dodders  or  love  vines  are  a  group  of  flowering 
plants  which  are  closely  related  to  the  Convolvulus 
or  Morning  glory  family.  Dodders  are  peculiar  in 
that  they  are  destitute  of  the  green  coloring  matter 
chlorophyll,  and  for  this  reason  must  lead  a  parasitic 
life.  The  plant  obtains  food  by  actually  sending  its 
own  roots  into  the  tissue  of  the  attacked  green  plant. 

The  Parasite.  When  the  dodder  seed  germinates 
it  is  at  first  able  to  support  itself  and  it  then  consists 
mainly  of  a  yellow,  threadlike  stem.  This  independ- 
ent existence  is  maintained  until  the  food  in  the  seed 
is  used  up.  By  this  time  the  young  tendril-like  plant 
attaches  itself  to  its  host  (fig.  17  a,  b)  and  sends  in 
suckers  or  feeders  which  penetrate  the  interior  tissue. 
The  attacked  plant  naturally  becomes  weakened  and 
may  even  die  as  a  result  of  being  robbed  of  its  food, 
which  is  taken  up  by  the  dodder.  After  reaching 
maturity,  the  parasite  blossoms  and  forms  seed  in  the 
usual  way  as  any  other  flowering  plant. 

Methods  of  Control.  Dodder  is  often  introduced  as 
seed  mixed  in  with  the  seed  which  we  buy.  By  care- 


FIG.  17.     DODDER. 

a.   Dodder  on  Tomato  plant,  b.  dodder  on  onion  leaves  (after  Ilalsted). 


Causes  of  Diseases  in  Crops          91 

ful  sifting,  the  dodder  seed  may  be  separated  out  from 
the  others.  Infested  areas  should  be  burned  over  so 
that  the  dodder  would  be  prevented  from  spreading 
and  producing  seed.  In  case  of  large  infested  spots  in 
the  field  it  may  be  necessary  to  use  drastic  measures. 
Each  trucker,  of  course,  could  best  decide  for  himself 
the  cheapest  and  speediest  way  of  eradicating  the  pest. 


CHAPTER  VII 

POOR  SEED 

IT  has  been  briefly  stated,  page  88,  that 
seeds  can  be  carriers  of  various  diseases.  The 
trucker  may  also  experience  difficulty  in  the  germi- 
nation of  seeds  which  may  be  accounted  for  in  many 
ways. 

Age  of  Seed.  In  determining  the  causes  of  poor 
germination  the  age  of  the  seed  is  to  be  considered,  for 
after  a  certain  age  limit  deterioration  sets  in.  With 
many  species  of  seeds  there  are  apparently  no  ex- 
ternal symptoms  to  indicate  loss  of  vitality  due 
to  age.  Each  seed  has  its  own  age  limit,  generally 
determined  by  the  character  of  the  seed  itself,  i.  e., 
whether  oily  or  starchy  or  lacking  in  both.  Thus  the 
vitality  of  the  minute  seed  of  tobacco  is  perhaps  eight 
times  as  great  as  that  of  the  large  oily  seed  of  the 
castor  bean. 

Cultural  Conditions.  The  viability  of  seed  is  also 
largely  determined^  by  the  conditions  under  which 
the  previous  crop  grew.  The  more  vigorous  the 
mother  plant  the  more  vitality  will  there  be  im- 
parted to  its  offspring.  The  vigor  of  the  previous 
crop  depends  on  favorable  climatic  conditions, 

92 


Poor  Seed 


93 


care  in  cultivation  and  in  fertilization.  Old  seed 
produced  in  a  favorable  season  may  be  preferred  to 
fresh  seed  but  of  an  inferior  quality,  produced  in  a 
bad  season. 

Weight  and  Color  of  Seed.  As  a  rule,  light  weight 
seed  is  inferior  to  heavy  seed  of  the  same  variety. 
The  weight  of  the  seed  is  influenced  by  culture  and  by 
imperfect  fertilization  which  results  in  minute  and 
weak  embryos.  The  weight  of  seed  may  be  readily 
determined  by  the  water  method.  Place  the  seed  in 
a  tumbler  filled  with  water.  After  shaking  and  let- 
ting it  stand  for  a  few  minutes,  the  heavy  ones  sink 
and  the  light  ones  float.  Using  this  method,  Stone1 
has  shown  that  the  heavy  sinking  seed  give  a  higher 
per  cent,  of  germination  than  the  lighter  (see  Tables  IO 
and  n). 

TABLE  10 

Showing  the  Results  of  Seed  Separation  by  the  Water  Method 


..- 

No.  of  Seeds  Germinated 

Name  of  Seed 

Per    Cent,  of  Increase  in 
Germination  of  Light 

Light 

Heavy 

over  Heavy  Seed 

Lettuce 

68 

90 

32. 

Onion 

100 

117 

17- 

Onion 

38 

85 

142. 

Lettuce 

44 

88 

100. 

Onion 

50 

58 

17. 

Average 

60 

87 

61. 

1  Stone,  G.  E.,  Massachusetts  Agr.  Expt.  Sta.  Bui.  121  :3-i4, 1908. 


94 


Diseases  of  Truck  Crops 
TABLE  n 


Showing  Results  of  Seed  Separation  by  the  Water  Method 

on  Germination  and  Growth  of  Seeds  of  Onions. 

Total  of  400  Seeds  Used 


Per  Cent,  of  Germination 

No.  of 
Plants 

Wt.  of  Plants 
(grams) 

Per  Cent,  of  Increase 
of  Heavy  over 
Light 

Total 

Average 

Heavy  (sank) 
Light  (floated) 

45-5 
19-5 

85 

38 

18.1 
5-9 

.213 
•155 

37-42 

The  color  of  the  seed  does  not  seem  to  have  any 
influence  on  the  germination.  Darker  colored  seed 
is  usually  preferred  to  the  lighter  of  the  same  variety. 
Color,  however,  depends  largely  on  the  degree  of 
ripeness. 

Storage  Conditions.  The  vitality  of  seed  is  greatly 
influenced  by  storage  conditions.  The  longest 
lived  seed  may  be  ruined  by  improper  storage. 
The  ideal  conditions  of  storage,  however,  are  not 
always  those  which  favor  germination.  Seed  should 
be  cured  or  dried  before  storing.  The  drier  it  is 
the  less  likely  it  is  to  spoil,  and  the  higher  will 
be  the  temperature  it  can  stand.  When  large 
quantities  of  seed  are  to  be  handled  by  the  trucker, 
it  is  advisable  to  build  a  seed  house.  The  seeds 
are  best  kept  in  strong  paper  or  cloth  bags  and 
placed  in  tin  cans. 


Poor  Seed  95 

Seed  Testing.  In  buying  seed  we  must  never  take 
it  for  granted  that  the  germination  will  be  perfect. 
To  make  sure,  a  sample  of  the  seed  should  be  tested 
for  germination  and  for  purity.  The  simplest  method 
is  to  sow  a  definite  number  of  seeds  in  a  shallow  pan 
filled  with  moist  sand. 

The  fact  that  a  seed  sprouts  does  not  always  mean 
a  full  stand  in  the  field.  Some  weak  seeds  may 
germinate  and  then  fail  completely  to  make  proper 
growth.  Allowance  must  be  made  for  this  possibility 
where  germination  tests  are  made  in  the  laboratory  or 
at  home.  In  testing  for  germination,  the  purity  of 
the  seed  is  also  to  be  considered.  As  a  rule  there  is 
no  danger  of  truck  seed  introducing  weeds,  due  to  the 
fact  that  vegetable  gardens  are  kept  in  a  clean  state 
of  cultivation.  The  honest  seedman  may  be  trusted, 
too,  to  screen  his  seed  carefully. 

Effect  of  Fertilizer  on  Seed.  With  the  hope  of 
hastening  germination,  truckers  apply  various  fer- 
tilizers to  the  seed  bed.  This  practice  cannot  be  too 
strongly  discouraged,  especially  when  muriate  of  pot- 
ash and  nitrate  of  soda  are  used.  These  two  fer- 
tilizers when  used  in  strengths  of  one  per  cent,  or  more 
inhibit  the  germination  of  the  seed,  whether  applied 
directly  or  mixed  with  the  soil.  Phosphoric  acid  or 
lime  when  not  used  in  excess  seem  to  have  no  injuri- 
ous action  on  germination.  However,  on  no  account 
should  commercial  fertilizers  be  brought  into  direct 
contact  with  the  seed.  The  injury  in  this  case  is  not 
apparent  on  the  seed  coat,  but  it  will  appear  on  the 
young  tender  sprouts.  Although  much  remains  to  be 


96 


Diseases  of  Truck  Crops 


investigated  as  to  the  effect  of  fertilizers  on  seed,  the 
work  of  Hicks1  will  serve  as  a  guide  to  the  trucker. 
Tables  12  and  13,  adapted  from  Hicks,  clearly  show  the 
effect  of  chemical  fertilizers  on  lettuce  and  radish  seeds. 

TABLE  12 

Effect  of  Chemical  Fertilizers  on  the  Germination  of  Curled 
Simpson  Lettuce  Seed 


Fertilizer  Used 

How  Applied 

First 
Sprouts 

Per  Cent. 
Germinated 
Fourth  Day 

Per  Cent. 
Germinated 
Twelfth  Day 

Potash 

In  the  rows 

No  sprouts 

No  sprouts 

Mixed  with  the  soil 

«i         «< 

««         « 

Phosphoric 

In  the  rows 

May  26 

«         <i 

2-5 

acid 

Mixed  with  the  soil 

"      21 

2-5 

45.25 

Nitrogen 

In  the  rows 

No  sprouts 

No  sprouts 

Mixed  with  the  soil 

««         «i 

(i         « 

Lime 

In  the  rows 

May  23 

o-75 

36.0 

Mixed  with  the  soil 

"      22 

4.00 

39-75 

Mixed 

In  the  rows 

No  sprouts 

No  sprouts 

fertilizer 

Mixed  with  the  soil 

u         «« 

(i         « 

Check, 

no  fertilizer 

May  21 

40-5 

73-0 

TABLE  13 

Effect  of  Chemical  Fertilizers  on  the  Germination  of  Break- 
fast Radish  Seed 


Fertilizer  Used 

How  Applied 

First  Sprouts 

Per  Cent,  of 
Germination 

Potash 
Phosphoric  acid 

In  the  rows 
Mixed  with  the  soil 
In  the  rows 
Mixed  with  the  soil 

No  sprouts 
«         « 

May  26 
24 

i-5 
i-5 

IO.O 

95-0 

1  Hicks,  G.  H.,  U.  S.  Department  of  Agr.,  Div.  of  Botany.,  Bui. 
24:5-15,  1900. 


Poor  Seed 

TABLE    13 — (Continued) 


97 


Fertilizer   Used 

How  Applied 

First  Sprouts 

Per  Cent,  of 
Germination 

Nitrogen 
Lime 
Mixed  fertilizer 
Check,  no  fertilizer 

In  the  rows 
Mixed  with  the  soil 
In  the  rows 
Mixed  with  the  soil 
In  the  rows 
Mixed  with  the  soil 

May  25 
44     26 
May  24 

May  25 
24 
May  24 

2.O 

6-5 

37-5 
93-0 

34-5 
92.0 

96.5 

TREATMENT  OF  SEED  AGAINST  INSECT  INJURY.  In 
storage,  the  greatest  enemies  of  the  seed  are  weevils. 
These  feed  on  any  part  of  the  seed  lobes  or  embryo, 
thus  impairing  the  germinating  power.  Weevils  and 
other  seed-feeding  insects  may  be  destroyed  by  fumi- 
gating the  seed  house,  the  bin,  or  the  seed  can,  with 
carbon  bisulphide  used  at  the  rate  of  three  pounds  to 
each  thousand  cubic  feet  of  space.  The  carbon  bisul- 
phide is  placed  in  a  dish  on  top  of  the  seed  and  allowed 
to  evaporate.  The  fumes,  which  are  heavier  than  air, 
fall  to  the  bottom.  The  seed  house  or  bin  should  be 
made  air-tight  for  twenty-four  hours  during  fumiga- 
tion, and  all  fires  including  lighted  pipes  should  be 
kept  away  for  fear  of  an  explosion. 

A  new  and  safer  fumigant,  para-dichlorobenzene, 
has  recently  been  placed  on  the  market.  This  is  less 
poisonous  when  inhaled  than  carbon  bisulphide.  For 
each  hundred  cubic  feet  of  space,  twelve  ounces  of  the 
former  are  dissolved  in  water.  The  liquid  is  soaked 
in  rags  which  are  placed  in  the  air-tight  seed  house  or 
bins  to  be  fumigated. 


98      Diseases  of  Truck  Crops 

Seed  beds  are  very  often  attacked  by  mole  crickets. 
They  may  be  kept  out  by  a  wire  gauze  floor.  When 
the  seed  bed  is  made  and  the  earth  is  dug  out  to  a 
depth  of  one  foot  or  more,  a  sheet  of  galvanized  or 
copper  mosquito  netting  is  placed  at  the  bottom,  com- 
ing up  at  the  sides,  and  projecting  a  couple  of  inches 
above  ground.  Ants,  too,  are  often  destructive  to 
seed  beds.  They  feed  on  the  seed  and  carry  it  away 
to  their  nests.  This  is  especially  true  with  lettuce 
seed.  Ants  are  best  controlled  by  pouring  half  a 
pint  of  carbon  bisulphide  in  each  nest  and  immedi- 
ately plugging  its  entrance. 

OTHER  SEED  TREATMENT.  Since  seed  may  be  a 
carrier  of  diseases,  it  is  essential  that  we  have  a 
method  of  treatment  capable  of  destroying  the  dis- 
ease-producing organism  in  its  initial  stage.  Ex- 
posing the  seed  in  hot  water  at  various  degrees  of 
temperature  is  effective  in  controlling  certain  smuts  of 
grains.  Treating  the  seed  with  sulphuric  acid  accel- 
erates the  germination  of  certain  hard  seed,  destroy- 
ing at  the  same  time  spores  of  fungi  which  may  adhere 
to  the  exterior  of  the  epidermis.  Unfortunately 
there  have  been  no  extensive  trials  made  of  the  effect 
of  hot  water  and  sulphuric  acid,  in  accelerating  the 
germination,  and  preventing  the  diseases  which  are 
carried  on  or  within  the  seed  of  truck  crops.  How- 
ever, the  treatment  of  seed  (especially  tubers)  with 
corrosive  sublimate  or  formaldehyde  is  now  exten- 
sively practiced.  Where  the  soil  in  the  bed  is  ster- 
ilized, seed  treatment  becomes  necessary.  With  the 
exception  of  tubers  or  roots,  seeds  should  preferably 


Poor  Seed  99 

be  treated  in  formaldehyde.  Manns1  recommends 
that  before  planting,  all  seed  should  be  soaked  for 
twenty  minutes  in  a  solution  of  one  part  of  formalde- 
hyde in  320  parts  of  water,  i.  e.,  i  oz.  of  40  per  cent, 
formaldehyde  in  22  gallons  of  water.  The  cost  of 
this  treatment  is  very  small, 

1  Manns,  T.  F.f  Ohio  Agr.  Expt.  Sta.  Bui.  228  :  255-297,  1911. 


PART  III 


101 


CHAPTER  VIII 
SPECIFIC  DISEASES  OF  TRUCK  CROPS 

FAMILY  AGARICACE^E 

IN  this  important  family  of  fungi  we  may  consider 
the  ordinary  cultivated  mushroom,  Agaricus  campes- 
tris.  Few  truckers  as  yet  grow  mushrooms  on  a  large 
scale ;  but  as  food  is  getting  scarce  and  its  prices  soar- 
ing higher,  more  attention  will  no  doubt  be  paid  to 
this  important  crop. 

DISEASES    OF    THE    MUSHROOM    (Agaricus 
campestris  L.) 

Mushrooms  are  subject  to  few  diseases.  There  are 
but  two  which  need  concern  the  grower. 

BACTERIAL  SPOT 
Caused  by  Pseudomonas  fluorescens  (Fl.)  Mig. 

This  disease,  although  serious,  seems  to  be  re- 
stricted as  yet  to  the  mushroom  caves  in  St.  Paul,  Min- 
nesota. The  trouble  was  first  described  by  Tolaas. r 

Symptoms.     It  is  characterized  by  an  unsightly 

'  Tolaas,  A.  S.,  Phytopath.  5  :  51-53,  1915. 

103 


Diseases  of  Truck  Crops 


spotting  of  the  caps,  the  severity  of  which  differs  with 
the  cultivated  varieties,  especially  the  large  white 
kinds.  The  spots,  which  do  not  extend  deep  into  the 
flesh,  appear  while  the  mushroom  is  in  the  but- 
ton stage,  or  when  the  cap  is  fully  expanded.  The 
spots  are  pale  yellow,  becoming  a  chocolate  brown. 
Though  the  disease  does  not  seem  to  reduce  the 
yield,  the  market  value  of  the  spotted  mushrooms 
is  considerably  reduced. 

The  Organism.  Pseudomonas  fluorescens  is  a 
small  rod  rounded  at  both  ends  and  motile  by  means 
of  polar  flagella.  It  is  a  facultative  anaerobe;  pro- 
duces no  endospores,  no  gas,  but  liquifies  gelatine. 
On  beef  and  potato  agar  it  produces  a  shiny  grayish 
white  growth  accompanied  by  a  greenish  pigmenta- 
tion, which  diffuses  in  the  substratum. 

Control.  Spraying  the  mushroom  caps  with  solu- 
tions of  benetol,  sodium  carbonate,  or  copper  sul- 
phate seems  to  have  no  beneficial  effect.  On  the 
other  hand,  fumigating  the  beds  with  sulphur  before 
planting  the  spawn  insures  the  production  later  of  a 
clean  crop  of  mushrooms.  The  amount  of  sulphur 
to  use  is  about  one  and  a  half  pounds  to  each  thou- 
sand cubic  feet  of  cave  space. 

THE  MYCOGONE  DISEASE 
Caused  by  Mycogone  perniciosa  Mag. 

The  Mycogone  is  a  very  destructive  mushroom 
disease.  The  exact  amount  of  its  distribution  in  the 


FIG.  18.    MYCOGONE  DISEASE  OF  MUSHROOMS.    (AFTER  VEIHMEYER.) 


Family  Agaricaceae  105 

United  States  is  as  yet  unknown.  However,  if  once 
introduced  in  a  cave,  it  is  likely  to  ruin  the  entire 
crop. 

Symptoms.  The  symptoms  of  the  disease  are  often 
various.  The  presence  of  the  malady  may  be  indi- 
cated by  small  tubercules  on  the  cap  and  by  a  form 
of  fluffy  white  growth  on  the  gills,  which  interferes 
with  their  normal  development  (fig.  18).  The  result 
is  distorted  caps  and  stipes  and  finally  a  general 
darkening  and  decay  of  the  tissue.  In  severe  cases 
monstrous  soft  masses  with  thick  white  fungus  coat- 
ings are  observed  in  houses  in  which  the  disease  is 
very  prevalent.  In  this  case  the  affected  plants  have 
little  resemblance  to  mushrooms.  They  decay  rap- 
idly, and  emit  a  very  disagreeable  odor. 

The  Organism.  The  spores  of  Mycogone  perniciosa 
are  very  characteristic.  They  consist  of  two  cells,  the 
upper  spherical,  rough,  and  covered  with  warts,  the 
lower  hyaline,  smooth.  Both  cells  possess  a  thick  wall. 

Control.  According  to  Veihmeyer,1  there  are  no 
evidences  that  tend  to  show  that  the  Mycogone 
disease  is  carried  with  the  spawn  manufactured  by  the 
"tissue  culture"  method.  It  is  very  probable,  how- 
ever, that  the  disease  was  introduced  into  this  coun- 
try from  France  with  imported  virgin  spawn 
collected  at  random  from  fields.  The  disease  may  be 
introduced  into  a  new  place  with  the  manure  and 
then  spread  quickly  in  a  number  of  ways.  Immedi- 
ate temporary  measures  are  essential  for  the  control 
of  this  trouble.  Diseased  plants  when  first  noticed 

1  Veihmeyer,  F.  J.,  U.  S.  Dept.  of  Agr.  Bui.  127  :  1-24,  1914. 


io6  Diseases  of  Truck  Crops 

should  be  pulled  out  and  disposed  of  by  fire.  Allow- 
ing these  infected  plants  to  decay  in  the  beds  is  a  sure 
means  of  spreading  the  fungus  broadcast  in  the  cave. 
The  gain  from  keeping  the  beds  free  from  diseased 
specimens  will  more  than  compensate  for  the  trouble. 
At  the  end  of  the  season  the  beds  should  be  thor- 
oughly cleaned,  the  manure  should  be  carried  away 
to  a  distance  where  mushrooms  will  not  be  grown, 
although  it  may  be  used  for  garden  purposes,  since 
the  Mycogone  disease  is  only  known  to  attack  mush- 
rooms. After  the  cave  has  been  thoroughly  cleaned 
out,  it  should  be  disinfected  with  the  formaldehyde 
gas  method.  This  is  carried  out  as  follows:  For 
every  thousand  cubic  feet  of  cave  space  use  three 
pints  of  formaldehyde  and  twenty-three  ounces  of 
potassium  permanganate.  The  potassium  perman- 
ganate is  placed  in  two  or  three  earthen  or  wooden 
vessels,  each  having  a  capacity  of  one  quart  for  every 
ounce  of  permanganate.  When  ready  for  the  opera- 
tion, the  mushroom  house  is  sprinkled  with  water, 
the  potassium  permanganate  placed  in  the  recep- 
tacles, the  formaldehyde  poured  evenly  over  the 
permanganate,  and  the  cave  doors  closed  at  once. 
They  are  kept  closed  for  twenty-four  hours  and  then 
opened  to  allow  the  formaldehyde  fumes  to  escape. 
All  lights  must  be  kept  away  from  the  caves  while 
they  are  being  fumigated  since  formaldehyde  gas 
explodes  when  coming  in  contact  with  fire.  Mush- 
room houses  thus  treated  may  be  thoroughly  rid  of 
the  Mycogone  disease,  but  care  must  be  taken  to 
prevent  reinfection. 


Family  Agaricaceae  107 

It  is  hardly  necessary  to  add  that  all  tools  and 
wagons  which  were  used  in  connection  with  the  pre- 
viously infected  caves  should  be  disinfected  before 
being  used  again.  All  such  tools  and  vehicles  should 
be  washed  in  a  solution  of  one  pint  of  formaldehyde 
in  twenty  gallons  of  water.  In  all  these  operations 
extreme  care  is  necessary  for  the  man  who  operates 
not  to  inhale^  any  of  the  poisonous  formaldehyde 
fumes. 


CHAPTER  IX 

FAMILY  ARALIACE^E 

THE  ginseng  is  the  only  plant  in  this  family  which 
is  of  economic  importance.  Although  not  exactly 
a  truck  crop,  it  is  nevertheless  grown  by  truckers. 
The  distribution  of  the  crop  is  limited.  According 
to  the  Thirteenth  Census  of  the  United  States,  the 
area  devoted  to  ginseng  in  1909  was  23  acres,  and  the 
total  crop  valued  at  $151,888.  The  23  acres  are 
distributed  in  the  following  States:  New  York,  Wis- 
consin, Missouri,  Ohio,  Pennsylvania,  and  Michigan. 

DISEASES  OF  THE  GINSENG  (Panax 
quinguefolium) 

Ginseng  is  subject  to  numerous  diseases,  most  of 
which  may  be  kept  in  check. 

DAMPING  OFF  (Fie.  19  a),  see  PYTHIUM 

DOWNY  MILDEW 
Caused  by  Phytophthora  cactorum  (C.  and  L.)  Sch. 

Downy  mildew  is  a  destructive  disease  and  is 
found  wherever  ginseng  is  grown.  It  attacks  all 
parts  of  the  plant,  rendering  it  useless. 

108 


FIG.  19.    GINSENG  DISEASES. 

a.  Damping  off,  b.-c.  Phytophthora  mildew  on  leaf  and  root,  d.  Phytophthora 
mycelium,  e.  germination  of  conidia  by  means  of  zoospores,  /.  germination  of  conidia 
by  means  of  germ  tubes,  g.  sexual  fertilization  of  the  female  oogonium  by  the  male 
antheridium,  h.  germinating  oospore  by  means  of  a  germ  tube,  i.  cross  section  of  a 
root  infected  with  Acrostalagmus  showing  diseased  condition  of  nbro-vascular 
bundles,  k.  fruiting  stalks  of  Acrostalagmus  and  sclerotia  of  same,  /.  cross  section  of 
root  to  show  presence  of  mycelium  of  Acrostalagmus  in  vascular  bundles,  m.  papery 
leaf  spot,  n.  Alternaria.  blight  on  leaf,  o.  Alternaria  spore,  p.  black  rot  showing  fruit- 
ing cup  of  Sclerotinia  panacis  (d.  e.  f.  g.,  and  h.  after  Rosenbaum,  the  other  figures 
after  Whetzel  and  Rosenbaum). 


Family  Araliaceae  109 

Symptoms.  The  disease  first  attacks  the  petioles, 
resulting  in  the  drooping  of  the  leaflets.  In  severe 
cases,  the  leaf  stalks  are  killed  at  the  base  where  they 
join  the  stem.  This  causes  the  leaves  to  droop  over 
the  stem.  The  diseased  areas  usually  become  soft 
and  slimy.  On  the  leaves,  the  spots  are  dark  green, 
watersoaked,  and  bent,  soon  becoming  dry  white  in 
the  center  with  a  prominent  dark  green  water-soaked 
margin  (fig.  19  b).  In  wet  weather,  the  disease  at- 
tacks the  stem,  and  from  there  works  downward  to 
the  root  causing  it  to  decay  (fig.  19  c). 

The  Organism.  The  mycelium  (fig.  19  d)  of  Phy- 
tophthora  cactorum  somewhat  resembles  P.  infestans, 
the  cause  of  late  blight  of  the  Irish  potato,  but  differs 
from  it  in  producing  an  abundance  of  sexual  or  oos- 
pores  (fig.  19  g)  within  the  dead  tissue.  The  oospores 
pass  over  the  winter  unaffected  by  cold  weather.  In 
the  spring  they  germinate,  each  sending  out  a  germ 
tube  (fig.  19  h)  which  later  may  bear  from  one  to 
two  conidia.  These  as  claimed  by  Rosenbaum1 
may  germinate  by  means  of  a  germ  tube  or  by 
swarm  spores.  The  conidia  germinate  in  the  same 
way  (fig.  19  e  and  f). 

Control.  Downy  mildew  may  be  controlled  by 
spraying  with  3-3-50  Bordeaux.  Diseased  plants 
should  be  pulled  out  and  destroyed  by  fire.  Plant- 
ing the  roots  deep  in  the  soil  will  also  protect  them 
from  rotting.  This  seems  to  prevent  the  working 
downward  of  the  disease  from  the  stem  to  the  roots. 

Rosenbaum,  J.,  New  York  (Cornell)  Agr.  Expt.  Sta.  Bui.  363: 
65-106,  1915. 


1 10  Diseases  of  Truck  Crops 

WHITE  ROT 
Caused  by  Sclerotinia  liber tiana  Fckl. 

White  rot,  although  fairly  destructive,  attacks  only 
isolated  individual  plants.  It  is  prevalent  in  New 
York,  Ohio,  Michigan,  and  Wisconsin.  The  same 
disease  also  attacks  cucumbers  and  numerous  other 
crops  later  mentioned. 

Symptoms.  The  disease  usually  appears  during 
continuous  damp  weather.  It  attacks  the  plant  at 
its  stem  end  near  the  soil  line.  The  infected  part 
becomes  soft,  watersoaked,  bleached,  and  overrun  by 
a  white  weft  of  mycelial  growth  on  the  surface  of  the 
epidermis.  Later  sclerotia  or  dark  masses  of  fungal 
threads  appear  irregularly  within  the  pith  and  on  the 
surface  of  the  diseased  crown.  Infected  plants  wilt, 
topple  over,  and  collapse.  For  a  description  of  the 
causal  organisms,  see  lettuce,  p.  143. 

Control.  Spraying  will  not  control  this  disease. 
Whetzel  and  Rosenbaum1  suggest  that  the  soil  be  well 
drained,  and  that  plenty  of  ventilation  be  given  the 
shacks.  The  disease  may  also  be  eradicated  in  the 
same  manner  as  prescribed  for  lettuce  drop,  p.  144. 

BLACK  ROT 
Caused  by  Sclerotinia  panacis  Rank. 

Black  rot  is  not  as  prevalent  as  white  rot  above 
mentioned.  The  disease  was  named  and  described 
by  Rankin.2 

1  Whetzel,  H.  H.,  and  Rosenbaum,  J.,  U.  S.  Dept.  of  Agr.,  Bur, 
of  PI.  Ind.,  Bui.  250  :  7-44,  1912. 

3  Rankin,  W.  H.,  Phytopath.  2  :  28-31,  1912. 


Family  Araliaceae  in 

Symptoms.  Black  rot  is  apparently  a  root  disease 
only.  Roots  dug  from  affected  areas  are  coal  black, 
with  no  rootlets,  but  with  intact  bud,  which,  however, 
is  also  blackened  like  the  root.  On  the  surface  of  the 
latter  are  found  numerous  sclerotia  the  size  of  a  small 
pea.  On  cutting  open  a  diseased  root  only  the  outer 
rind  is  found  to  be  blackened,  while  the  center  re- 
mains white,  spongy,  and  watery.  The  affected  root 
does  not  soft  rot,  but  becomes  very  bitter  in  taste. 
If  left  over  in  the  soil  for  two  seasons  the  root  will 
turn  black  all  through,  shriveling  and  decaying. 
Black  rot  works  only  in*  cold  weather  of  early  spring 
or  late  fall.  In  structure  Sclerotinia  panaois  greatly 
resembles  S.  liber tiana  (fig.  19  p). 

Control.  Remove  the  diseased  plants  and  the  sur- 
rounding healthy  ones  on  a  strip  a  foot  wide.  Drench 
the  soil  with  a  heavy  application  of  one  part  com- 
mercial formaldehyde  in  50  parts  of  water — about  I 
gallon  per  sq.  ft. 

FIBER  ROT  (RUST) 
Caused  by  Thielavia  basicola  (B.  and  Br.)  Zopf. 

Symptoms.  The  manifestations  of  fiber  rot  depend 
largely  on  the  age  of  the  root  and  the  part  attacked. 
With  seedlings  and  in  dry  weather  the  leaves  lose 
their  dark  green  color,  become  pale,  tinting  into 
shades  of  red,  and  finally  the  leaflets  wither  and  the 
stems  wilt.  Often  the  leaves  of  infected  seedlings 
take  on  a  purple  bronze  color.  In  wet  weather  the 


ii2  Diseases  of  iruck  Crops 

wilting  is  more  sudden,  and  the  stems  bend  into  a 
curve.  In  this  case  affected  seedlings  seem  to  preserve 
their  natural  green  color.  The  disease  is  confined 
to  the  root  fibers,  which  turn  rusty  brown  or  black. 
In  severe  cases,  all  that  is  left  is  a  charred  stub. 
The  affected  tissue  is  dry,  although  several  soft  rots 
may  follow  the  primary  injury.  For  a  description 
of  the  causal  organism  see  garden  pea,  p.  275. 

Control.  For  seed  beds  the  soil  should  be  treated 
with  steam  or  formaldehyde  as  described  in  pages 
53~59-  For  large  beds  the  application  of  acid  phos- 
phate at  the  rate  of  one  thousand  pounds  per  acre 
will  be  found  beneficial.  The  treatment,  to  be  effec- 
tive, must  be  given  to  soils  not  too  alkaline.  Where 
the  soil  is  strongly  alkaline,  heavier  quantities  of 
acid  phosphate  should  be  applied,  so  that  the  treated 
soil  may  become  distinctly  acid. 

STEM  ANTHRACNOSE 
Caused  by  Vermicularia  dematium  (P.)  Fr. 

Symptoms.  Anthracnose  is  apparently  a  seedling 
disease  of  little  importance.  It  appears  as  numerous 
black  spots  on  the  stems  of  the  young  plants.  These 
enlarge  and  very  frequently  end  by  girdling  and  kill- 
ing the  entire  stem. 

Control.  The  disease  may  be  controlled  by  spray- 
ing with  Bordeaux  mixture  as  soon  as  the  plants  are 
about  three  weeks  old.  Spraying  should  be  repeated 
every  two  to  three  weeks  until  about  August  ist. 


Family  Araliaceae  113 

LEAF  ANTHRACNOSE 

Caused  by  Pestalozzi a  funerea  Desm. 

Symptoms.  This  malady  attacks  the  base  of  the 
leaves  and  flower  stalks.  It  results  in  an  early  drop 
of  the  foliage  which  also  indirectly  affects  the  roots. 
Spraying  with  Bordeaux  is  said  to  control  this 
trouble. 

ACROSTALAGMUS   WlLT 

Caused  by  Acrostalagmus  panax  Ran. 

This  wilt  seems  to  be  destructive  only  in  the  spring 
of  the  year.  It  is  prevalent  wherever  ginseng  is 
growing. 

Symptoms.  The  first  evidence  of  the  disease  is  a 
slow  drying  and  wilting  of  isolated  plants  here  and 
there  in  the  field.  At  first  the  leaves  droop,  suggesting 
a  lack  of  water  in  the  soil.  This,  however,  is  not  the 
case.  Outwardly  the  roots  of  affected  plants  appear 
sound,  but  on  cutting  open  one  of  these  the  fibro- 
vascular  bundles  will  be  found  to  be  yellowed,  indicat- 
ing the  presence  of  the  fungus  within  (fig.  19  i  and  1). 
The  spores  of  the  fungus  are  very  minute  and  are 
formed  on  slender  branched  stalks  (fig.  19  k)  which 
appear  on  the  surface  of  such  decayed  stems  or  roots. 
The  fungus  also  produces  sclerotial  like  bodies  (fig. 
19  k)  which  apparently  serve  in  tiding  it  over  un- 
favorable weather  conditions.  The  fungus  has  been 
identified  by  Rankin1  as  Acrostalagmus  panax.  So 

1  Rankin,  W.  H.,  Spec.  Crops.  U.  S.,  9  :  349,  1910. 


ii4  Diseases  of  Truck  Crops 

far  as  is  known,  no  definite  method  of  control  can  be 
recommended.  The  use  of  healthy  roots  should  be 
depended  upon.  Wherever  possible  soil  sterilization 
with  steam  or  formaldehyde  is  also  recommended. 

ALTERNARIA  BLIGHT 
Caused  by  Alter naria  panax  Whet. 

Blight  is  perhaps  the  most  common  of  all  ginseng 
diseases.  It  is  found  practically  wherever  this  crop 
is  grown. 

Symptoms.  The  disease  at  first  manifests  itself 
as  dark  brown  spots  on  one  side  of  the  stem.  Often 
the  spots  work  in  deep  and  cause  the  stem  to  rot  and 
break  at  the  point  of  the  lesion.  On  the  leaves, 
blight  appears  as  watersoaked  spots.  These  grad- 
ually dry  out,  becoming  thin  and  papery  with  a 
distinct  rusty  brown  border  (fig.  19  n).  The  disease 
may  also  attack  the  leaflets  at  the  point  of  attach- 
ment to  the  leaf  stalk.  This  generally  causes  a 
dropping  and  dying  of  the  leaflets.  Later  a  velvety 
brown  cover  appears  on  the  dead  tissue  which  con- 
sists of  the  spores  of  the  fungus.  Frequently  the 
seed  heads  are  also  infected. 

The  Organism.  The  mycelium  of  Alternaria  panax 
is  brown,  septate.  The  conidiophores  are  erect, 
brown,  septate,  irregular  at  the  tips,  and  tufted. 
The  conidia  are  brown,  borne  in  chains,  and  typical 
of  Alternaria  (fig.  19  s). 

Control.  Blight  may  be  effectively  kept  in  check 
by  spraying  with  a  3-3-50  Bordeaux  mixture. 


Family  Araliaceae  115 

Strong  solutions  will  not   injure  the  plants  but  are 
unnecessary. 

ROOT  KNOT,  see  NEMATODE 

PAPERY  LEAF  SPOT 
Caused  by  drought. 

Symptoms.  The  trouble  appears  as  thin,  papery 
whitish  to  yellowish,  transparent  spots  between  the 
veins  and  along  the  margins  of  the  leaves.  This 
spotting  is  often  mistaken  for  Bordeaux  injury  or 
for  Alternaria  blight. 

Cause.  Papery  leaf  spot  is  brought  about  by  a 
lack  of  sufficient  moisture  in  the  soil.  Drought,  large 
tree  roots  in  the  beds,  or  insufficient  shading  may 
deprive  the  plants  of  the  amount  of  soil  moisture 
which  they  require.  Control  measures  should  con- 
sist in  eliminating  as  far  as  possible  those  factors 
which  are  conducive  to  drought. 

BORDEAUX  INJURY 

This  form  of  injury  is  brought  about  when  spray- 
ing with  Bordeaux  mixture  which  is  followed  by  frost. 
Affected  plants  appear  scalded,  soft  rot,  and  finally 
they  dry  and  become  papery  (fig.  19  m).  As  a  pre- 
caution plants  should  not  be  sprayed  during  periods 
when  frost  is  predicted. 


CHAPTER  X 

FAMILY   CHENOPODIACE^E 

THIS  family  comprises  the  beet,  chard,  spinach,  and 
the  Strawberry  Elite.  The  latter  is  not  generally 
known  to  American  truckers.  In  England  it  is  culti- 
vated as  a  pot  herb.  The  first  three,  however,  are  ex- 
tensively grown  in  home  gardens  on  a  small  scale,  or  in 
trucking  on  a  large  scale  for  market.  According  to  the 
Thirteenth  Census  of  the  United  States  the  1909  area 
in  beets  was  3202  acres,  New  York  leading  with 
834  acres  to  her  credit.  The  States  which  follow 
according  to  rank  are:  Massachusetts,  California, 
Louisiana,  Illinois,  Pennsylvania,  New  Jersey,  and 
Michigan.  The  remaining  States  each  devote  a 
very  limited  acreage  to  beets  and  are  hence 
omitted.  The  area  devoted  to  spinach  in  the 
United  States  in  1909  was  6668  acres.  Of  the  leading 
States  in  the  production  of  this  crop  may  be  es- 
pecially mentioned  Virginia  with  3058  acres.  The 
other  spinach  States  are  classified  according  to  rank 
as  follows:  Maryland,  New  York,  New  Jersey,  Mas- 
sachusetts, Illinois,  and  Pennsylvania.  The  money 
value  in  the  United  States  of  the  beet  crop  in  1909 
was  $352,696  and  of  the  spinach  crop  $817,069. 

116 


Family  Chcnopodiaceae  117 

We  have  no  available  statistics  of  the  money  losses 
to  beets  and  spinach  from  the  various  diseases  about 
to  be  mentioned. 

DISEASES  OF  THE  BEET  (Beta  vulgar  is) 

Beets  are  subject  to  numerous  diseases,  some  of 
which  are  of  great  economic  importance,  while  others 
are  insignificant  and  need  not  be  feared  by  the  trucker 
or  gardener. 

WATER-CORE  SPOTS 
Cause  unknown. 

Arthur1  has  described  a  disease  of  beets  which  he 
named  water-core  spots. 

Symptoms.  The  disease  is  characterized  by  well 
defined  spots  in  the  interior  of  the  root.  These 
spots  greatly  resemble  the  water-core  spots  of  the 
apple.  The  spots  generally  occur  between  the 
fibrous  rings.  They  are  sharply  defined  and  do 
not  grade  into  the  adjoining  tissues.  The  spots 
range  from  a  pin-head  to  half  an  inch  in  size, 
and  resemble  a  pea  in  shape.  Sometimes  there 
are  but  one  or  two  spots  in  the  root,  but  more 
generally  several  are  present.  The  disease  does 
not  seem  to  be  of  any  great  economic  importance, 
and  it  is  not  likely  that  any  financial  losses  will  be 
attributed  to  it. 

Arthur,  J.  C.,  Indiana  Agr.  Expt.  Sta.  Bui.  39,  vol.  3  :  54-62,  1892. 


n8  Diseases  of  Truck  Crops 

SOFT  ROT 

Caused  by  Bacterium  teutlium  Met. 

This  disease  was  originally  described  by  Metcalf . x 
It  is  not  known  whether  the  garden  beet  is  seriously 
affected  by  it.  The  trouble,  however,  is  of  economic 
importance  where  sugar  beets  are  grown  extensively. 

Symptoms.  The  disease  in  its  initial  stage  is  char- 
acterized by  a  soft  rot  at  the  lower  portion  of  the 
root.  At  this  stage  the  crown  and  leaves  remain 
normal,  but  later  the  outer  leaves  die  and  fall  off. 
The  disease  is  primarily  a  root  trouble;  the  decayed 
tissue  is  soft,  yellowish  gray,  and  contains  a  sour 
smelling  liquid  which  exudes  at  the  least  pressure. 
It  is  most  prevalent  in  wet  and  poorly  drained  lands. 
The  cause  of  soft  rot  is  a  bacterial  organism,  Bac- 
terium teutlium. 

Control.  Since  the  disease  works  on  the  root 
underground  it  is  clear  that  no  exterior  treatment 
will  be  effective.  Thorough  drainage,  careful  culti- 
vation, and  crop  rotation  are  the  only  methods  of 
control  known. 

CROWN  GALL 
Caused  by  Pseudomonas  tumefaciens  Sm.  and  Town. 

Crown  gall  is  a  very  important  disease  because  of 
its  cosmopolitan  nature.  It  prevails  widely  and 
attacks  a  large  number  of  hosts. 

1  Metcalf,  Haven,  Nebraska  Agr.  Expt.  Sta.  iyth  Ann.  Rept.:  69- 
112,  1904. 


FIG.  20.     BEET  DISEASES. 

a.  Crown  gall,  b.  scab,  c.  downy  mildew,  d.  Conidiophore  of  Peronospora  schachlii 
arising  from  a  stomate  of  an  infected  beet  leaf,  e.  germinating  zoospore  of  P.  schach- 
tii,f.  oospore  of  P.  schachtii,  g.  Cercospora  leaf  spot  (after  Halsted),  h.  conidiophore 
and  conidia  of  Cercospora  beticola  (after  Duggar),  i.  Phoma  leaf  spot  (after  Pool  and 
McKay),  k.  pycnidium  of  Phoma  beta  (after  T.  Johnson)  (d.-f.  after  Prillieux). 


Family  Chenopodiaceac  119 

Symptoms.  The  disease  does  not  usually  manifest 
itself  until  the  roots  are  nearly  half  grown.  Abnormal 
outgrowths  or  galls  (fig.  20  a)  appear  which  vary  in 
size  from  that  of  a  garden  pea  to  nearly  two  inches  in 
diameter,  depending  on  the  severity  of  the  attack. 
The  galls  are  usually  attached  to  the  beet  by  a  narrow 
string.  In  light  cases  of  infection  there  may  be  but 
one  gall  on  the  root;  in  severe  cases,  however,  the 
roots  may  be  covered  with  numerous  galls. 

The  Organism.  The  cause  of  crown  gall  is  a  bac- 
terial organism,  Pseudomonas  tumefaciens  Sm.  and 
Town.  It  is  a  short  rod,  multiplying  by  fission,  which 
moves  about  by  means  of  polar  flagella.  On  agar  or 
gelatine  it  forms  small  round  white  colonies.  Under 
unfavorable  conditions  it  readily  develops  involution 
forms;  in  pure  culture  the  organism  is  short  lived. 
P.  tumefaciens  lives  over  in  the  soil  from  year  to 
year. 

Control.  Although  crown  gall  is  known  to  attack 
a  large  number  of  plants,  it  has  never  been  found  as  a 
parasite  on  grain  crops.  Gardens  or  fields  which 
refuse  to  grow  beets  because  of  the  disease,  should  be 
given  a  rest  for  at  least  three  years  by  planting  sweet 
corn  instead.  According  to  Dr.  Smith1  the  follow- 
ing truck  crops  are  susceptible  to  crown  gall :  Tomato, 
potato,  cabbage,  beet,  radish,  and  salsify.  In  infected 
fields,  these  crops  should  be  left  out  when  planning  a 
rotation  which  is  aimed  at  starving  out  the  organism 
in  the  soil. 

'Smith,  E.  P.,  et.  al.,  "  Crown  Gall  of  Plants,"  U.  S.  Dept.  Agr., 
Bur.  PI.  Ind.,  Bui.  213  :  13-200,  1911. 


ri2o  Diseases  of  Truck  Crops 

TUBERCULOSIS 

Caused  by  Pseudomonas  beticola  Ew.  Sm. 

Tuberculosis  differs  from  the  crown  gall  by  the 
formation  of  small  tubercules  on  the  root.  The  part 
of  the  root  nearest  to  the  tubercule  is  brown  and 
watersoaked  and  broken  into  hollow  cavities.  The 
diseased  tissue  is  mucilaginous  and  stringy  when 
touched. 

The  Organism.  Tuberculosis  is  induced  by  an 
organism,  Pseudomonas  beticola.  In  pure  culture  of 
agar  the  colonies  are  circular,  smootji  or  wrinkled, 
and  in  color  are  yellow.  The  organism  is  rod  shaped, 
single  or  in  pairs,  and  moves  about  by  means  of  polar 
flagella. 

Control.  The  disease,  so  far  as  is  known,  does  not 
seem  to  be  of  any  economic  importance.  Diseased 
material  should  be  destroyed  by  fire  and  the  infected 
soil  soaked  with  formaldehyde  made  up  of  one  pint 
of  the  chemical  in  twenty  gallons  of  water  and  ap- 
plied at  the  rate  of  one  gallon  of  the  solution  to 
each  square  foot  of  space.  The  organism  seems 
able  to  gain  entrance  only  through  wounds.  Care 
is  therefore  necessary  to  prevent  cutting  or  bruising 
the  roots  during  cultivation  or  at  harvesting. 

SCAB 

Caused  by  Actinomyces  chromogenus  Gasp. 

Scab  on  beets  is  the  same  as  the  scab  of  the  Irish 
potato.  The  disease  is  of  the  greatest  economic  im- 


Family  Chenopodiacese  121 

portance  in  localities  where  potatoes  suffer  heavily 
from  the  disease. 

Symptoms.  The  symptoms  of  the  disease  on  beets 
(fig.  20  b)  do  not  differ  much  from  those  of  the  Irish 
potato  (see  p.  317).  Occasionally,  the  scabs  which 
arise  before  the  beet  is  full  grown  disappear  entirely, 
leaving  merely  a  small  scar.  This  is  somewhat 
sunken  and  has  a  definite  outline.  In  normal 
cases  of  infection,  the  scabby  areas  on  the  beet  are 
greater  in  area,  and  thicker ;  the  corky  layer  of  the 
spots  decidedly  bulging  out.  Immediately  below  the 
scabby  areas  the  tissue  is  a  discolored  reddish  brown. 

The  Organism.  The  cause  of  beet  scab  is  the  same 
as  that  of  the  scab  of  the  white  potato  (see  p.  317). 
The  parasite  is  a  soil  organism,  and  thrives  best  under 
alkali  conditions. 

Control.  Beets  should  not  grow  where  Irish  po- 
tatoes, carrots,  or  radish  are  known  to  suffer  from  the 
same  disease.  Lime  and  fertilizers  which  tend  to 
make  the  soil  alkaline  should  be  avoided. 

ROOT  TUMOR 
Caused  by  Urophlyctis  leproides  (P.  Mag.)  Trab. 

This  trouble  fortunately  is  as  yet  unimportant  in 
the  United  States.  The  disease  is  characterized  by 
the  formation  of  nodules  or  outgrowths  often  the  size 
of  a  walnut  on  the  rootlets  or  leaves.  The  fleshy 
root  itself  is  seldom  attacked.  The  tissue  of  the 
tumors  contains  numerous  cysts  or  spore-bearing 
cells. 


122  Diseases  of  Truck  Crops 

Control.  All  infected  plants  must  be  removed  or 
destroyed.  To  be  successful  this  must  be  done  early 
enough  before  the  winter  spores  of  the  fungus  are 
liberated  in  the  soil. 

DAMPING  OFF  AND  ROOT  ROT 

Caused  by  Pythium  de  Baryanum  Hess. 

Symptoms.  Damping  off  of  the  seedlings  just  as 
they  emerge  from  the  ground  is  often  a  common 
trouble  under  poor  cultural  conditions.  The  young 
seedlings  topple  over  and  die  in  the  characteristic 
way  so  familiar  to  truckers.  The  greatest  damage 
occurs  after  heavy  rains  when  a  hard  crust  is  formed 
on  the  surface  preventing  the  seedlings  from  emerg- 
ing normally.  On  old  and  mature  roots,  Pythium  de 
Baryanum  may  cause  a  rot.  According  to  Clinton, r 
the  disease  is  found  to  be  severe  on  mangels.  A 
peculiarity  of  the  rot  is  that  it  seldom  starts  at  the 
top  of  the  crown.  The  latter  appears  to  be  perfectly 
healthy,  although  the  leaves  turn  yellow,  indicating 
a  diseased  condition  further  down.  Rotted  roots 
are  found  to  be  overrun  by  a  varied  flora,  although 
Pythium  de  Baryanum  is  the  original  cause  of  the 
trouble.  For  a  further  description  of  the  organism 
see  p.  43. 

Control.  The  disease  is  more  prevalent  during  wet 
weather,  and  in  heavy  soils  which  are  poorly  drained. 
Thorough  drainage  of  the  land  and  careful  cultiva- 

1  Clinton,  G.  P.,  Connecticut  Agr.  Expt.  Sta.  39th.  Ann.  Rept. : 
433-436, 


Family  Chenopodiaceae  123 

tion  will  greatly  help  to  control  the  rot  on  the  ma- 
ture roots.  To  prevent  seedlings  from  damping  off 
care  should  be  taken  that  no  hard  crust  be  allowed  to 
form  on  the  soil.  After  a  rain  the  soil  should  be 
worked  as  soon  as  possible. 

WHITE  RUST 
Caused  by  Cystopus  bliti  (Biv.)  Lev. 

This  disease  is  of  little  economic  importance  as  far 
as  the  trucker  is  concerned.  Its  occurrence  on  beets 
has  been  reported  but  once  by  Pammel. J  In  appear- 
ance, infected  leaves  show  white  raised  pustules  or 
sori  on  the  under  side.  When  the  surface  cover  of 
the  pustules  bursts  open  a  powdery  mass  of  snow- 
white  spores  is  liberated.  The  same  disease  also 
attacks  '  *  pigweeds. ' '  Clean  culture  is  recommended . 

DOWNY  MILDEW 
Caused  by  Peronospora  schachtii  Fckl. 

This  disease,  like  white  rust,  is  of  little  economic 
importance  in  the  United  States.  The  trouble, 
however,  is  very  prevalent  in  Europe.  The  mildew 
attacks  the  young  seedlings  in  grayish  patches  on 
the  under  side  of  the  foliage.  On  older  plants  the 
mycelium  of  the  causative  fungus  works  down- 
wards into  the  root  where  it  is  carried  over  winter 

(fig.  20C-f). 

1  Pammel,  L.  H.,  Iowa  Agr.  Expt.  Sta.  Bui.  15  :  234-254,  1891. 


124  Diseases  of  Truck  Crops 

DROP 

Caused  by  Sclerotinia  libertiana  Fckl. 

Drop  on  beets,  which  attacks  young  seedlings,  but 
not  older  plants,  is  otherwise  not  very  different  from 
a  similar  trouble  on  lettuce.  Clinton1  reports  a  case 
of  beet  drop  in  an  outdoor  seed  bed.  The  warm  con- 
dition of  the  soil,  soon  after  making  the  seed  bed, 
was  important  in  favoring  the  disease.  Sterilizing 
the  soil  with  formaldehyde,  careful  regulation  of 
soil  temperature  and  watering  are  methods  to  be 
observed  in  the  control  of  the  trouble. 

RUST 
Caused  by  Uromyces  beta  Kuhn. 

This  disease  has  been  reported  only  on  beets  in 
California.  In  Europe  it  is  especially  common  on 
the  wild  beet  (Beta  maritima) . 

The  Organism.  The  cause  of  this  rust  is  a  fungus, 
Uromyces  beta,  the  latter  having  three  spore  stages, 
all  of  which  occur  on  the  same  host,  but  at  different 
times  of  the  year. 

i.  Spring  or  Cluster  Cup  Stage.  This  is  seen  as 
small,  whitish,  raised  cups,  grouped  on  a  yellow  spot. 
When  opened,  these  cups  emit  a  yellowish  powder 
which  is  made  up  of  large  quantities  of  the  yel- 
low colored  aecediospores.  The  latter  germinate 

1  Clinton,  G.  P.,  Report  of  the  Botanist  for  1915,  Connecticut 
Agr.  Expt.  Sta.  39th  Ann.  Rept.  :  433-436,  1915. 


Family  Chenopodiaceae  125 

by  means  of  a  germ  tube  which  enters  the  beet  leaf 
again.  -2.  Uredo  Stage.  The  result  of  infection  from 
the  aecediospores  is  manifested  as  raised  small  pus- 
tules which  are  thickly  scattered  over  the  leaf. 
When  these  burst  open,  uredo  or  summer  spores  are 
liberated.  These  are  round,  one  celled,  and  spiny, 
and  the  cell  wall  is  perforated  at  several  places. 
3.  Teleutospore  Stage.  As  soon  as  infection  of  the 
beet  leaves  takes  place  as  a  result  of  the  penetration 
of  the  germinated  uredospore  infection,  other 
darker  pustules  are  formed.  These  when  rupturing 
liberate  the  winter  or  teleutospores,  which  are  one 
celled,  thick  walled,  smooth,  and  darker  in  color. 
Their  function  is  to  carry  the  fungus  over  winter. 
The  infection  from  the  teleutospores  the  following 
spring  again  results  in  the  cluster  cup  stage. 

Control.  It  is  doubtful  if  spraying  will  control  the 
beet  rust.  The  better  way  is  to  plow  deeply  under 
the  affected  leaves.  This  will  prevent  the  germina- 
tion of  the  teleutospores  in  the  spring. 

LEAF  SPOT  AND  HEART  ROT 
Caused  by  Phoma  betes  Frank. 

This  disease  is  more  prevalent  as  a  storage  rot, 
although  it  also  produces  a  leaf  spot  in  the  field. 
The  trouble  is  as  yet  of  little  economic  importance. 
It  is  not  certain  whether  this  rot  is  the  same  as  that 
described  by  Halsted1  as  root  rot  of  beet  which  he 
attributed  to  a  species  of  Phyllosticta. 

1  Halsted,  B.  D.,  New  Jersey  Agr.  Expt.  Sta.  Bui.  107  :  3-13,  1895. 


126  Diseases  of  Truck  Crops 

Symptoms.  It  is  characterized  by  minute  brown- 
ish spots  on  the  leaves  (fig.  20  i  and  k).  On  the  roots 
it  is  manifested  as  a  dry  black  rot  extending  deep  in 
the  interior.  The  outside  of  the  root  has  a  shrunken 
appearance  which  closely  follows  the  seat  of  the  inte- 
rior rotting. 

Control.  In  the  field,  the  disease  first  starts  in  the 
seed  bed.  Spraying  with  4-4-50  Bordeaux  is  recom- 
mended. Two  applications  may  suffice.  In  the 
field,  spraying  has  not  as  yet  given  promising  results. 
Clean  culture  and  rotation  will  eventually  free  a  field 
from  the  disease. 

The  disease  is  introduced  upon  the  seeds  which 
frequently  bear  the  fruiting  bodies  of  the  fungus.  It 
has  been  shown  that  disinfection  of  the  seed  will 
prevent  the  carrying  over  of  the  disease. 

LEAF  SPOT 
Caused  by  Cercospora  beticola  Sacc. 

There  is  perhaps  no  beet  disease  that  is  of  greater 
economic  importance  than  leaf  spot.  The  trouble  is 
well  known  to  truckers  and  it  seems  to  be  found  where- 
ever  beets  can  thrive. 

Symptoms.  The  disease  first  makes  its  appearance 
on  the  leaves  as  tiny  circular  whitish  spots.  These 
gradually  increase  in  size  and  assume  a  brownish 
color.  The  spots  soon  increase  in  numbers  and 
involve  the  entire  area  of  the  leaf  (fig.  20  g),  which 
becomes  dry  and  brittle.  Leaf  spots  attack  the  outer 


Family  Chenopodiaceae  127 

and  older  leaves.  As  the  inner  foliage  advances  in 
age,  it  becomes  infected  in  turn.  As  serious  as  the 
disease  may  appear,  it  never  kills  the  plant.  The 
result,  however,  is  noticeable  on  the  roots,  which  are 
undersized  and  elongated  instead  of  round.  Leaf 
spot  generally  appears  during  a  moist  spell  followed 
by  a  period  of  dry  weather.  The  disease  increases 
in  severity  as  the  plants  are  weakened  by  heat  and 
drought. 

The  Organism.  The  fungus,  Cercospora  beticola, 
like  most  fungi,  is  composed  of  a  vegetative  part  of 
mycelium  and  of  spores.  The  latter  are  microscopic 
in  size,  somewhat  needleshaped,  and  divided  by 
means  of  a  cross  wall  into  two  to  seven  cells  (fig. 
20  h).  Each  of  these  cells  may  germinate  by  send- 
ing out  a  threadlike  tube,  which  penetrates  the  leaves 
through  the  stomata.  The  spores  are  borne  on  a 
cluster  of  stalks  or  conidiophores,  at  the  base  of  which 
is  formed  a  small  stroma.  The  temperature  and  re- 
lative humidity  of  the  air  influences  the  production 
and  infection  of  conidia.  According  to  Pool  and 
McKay1  a  temperature  of  80  or  90  degrees  F.  with  a 
minimum  of  not  less  than  60  degrees  at  night  is  most 
favorable  to  the  production  of  conidia.  They  are, 
however,  checked  by  a  temperature  of  100  degrees  or 
higher,  or  of  50  to  80  degrees  F.  Conidia  are  gener- 
ally formed  on  the  lower  surface  of  the  leaves,  no 
doubt  because  these  are  subject  to  a  higher  humidity. 

Control.     For   practical   purposes   leaf  spot   may 

1  Pool  Venus,  and  McKay,  M.  B.,  U.  S.  Dept.  Agr.  Journ.  Agr. 
Research,  7  :  21-60,  1916. 


128  Diseases  of  Truck  Crops 

be  controlled  by  deep  fall  plowing  and  crop  rotation. 
No  hard  and  fast  system  of  rotation  can  be  laid  down 
for  the  trucker.  He  himself  must  be  the  best  judge. 
It  seems  that  the  conidia  of  the  fungus  are  unable  to 
live  over  winter.  The  parasite,  however,  winters 
over  as  mycelium  within  the  affected  leaves.  Deep 
plowing,  therefore,  not  only  improves  the  land  but 
will  also  help  to  bury  the  debris  of  infested  leaves, 
thereby  removing  the  fungus  as  a  source  of  infection 
for  the  following  year.  Spraying  will  also  help  to 
control  leaf  spot.  The  formula  recommended  is  4 
pounds  copper  sulphate,  4  pounds  fresh  slaked  lime, 
to  50  gallons  of  water.  To  succeed  in  keeping  the 
disease  in  check,  spraying  must  be  carefully  carried 
out.  The  leaves  should  be  thoroughly  coated  with 
the  mixture  both  from  the  upper  and  under  sides. 
Clean  culture  and  constant  cultivation  will  also  check 
leaf  spot.  This  will  tend  to  maintain  the  moisture 
in  the  soil,  at  the  same  time  preserving  the  vigor  of 
the  plant.  Any  operation  which  tends  to  weaken  the 
plant  will  also  favor  infection. 

ROOT  ROT 
Caused  by  Corticium  vagum  B.  and  C. 

This  disease  is  very  prevalent  in  the  United  States, 
attacking  a  large  number  of  truck  crops  in  which  the 
beet  is  included.  It  has  been  carefully  studied  by, 
Duggar  and  Stewart1  and  by  others.  It  produces 

1  Duggar,  B.  M.,  and  Stewart,  F.  C.,  New  York  (Cornell)  Agr. 
Expt.  Sta.  Bui.  1 86  :  50-76, 1901. 


Family  Chenopodiaceae  129 

a  damping  off  of  the  young  seedlings,  and^on  older 
plants  a  rotting  of  the  crown.  In  pulling  out  an 
infested  plant,  we  find  that  the  outer  leaves  are  dead 
and  dry,  while  the  inner  ones  are  somewhat  curled. 
The  roots  of  such  plants  invariably  are  rotted  at  the 
crown,  the  rot  generally  working  inwards  to  a  con- 
siderable extent.  The  peculiarity  of  this  disease  is 
that  the  lower  half  of  the  root  is  generally  sound. 
Frequently  the  rotted  crowns  are  also  found  to  be 
cracked  at  various  places.  Beets  thus  affected  are 
worthless  for  the  market.  This  condition  naturally 
indicates  a  sick  condition  of  the  soil,  due  to  the  pres- 
ence of  Khizoctonia  solani.  For  a  description  of  the 
fungus  see  p.  45. 

Control.  There  are  no  methods  of  control  known. 
The  factors  which  favor  the  trouble  are  poor  drain- 
age, an  excess  of  soil  moisture,  and  lack  of  sufficient 
aeration.  Every  step  taken  to  overcome  these  will 
in  a  degree  help  to  control  the  rot. 

ROOT  KNOT 
Caused  by  Heterodera  radicicola  (Greef)  Muller. 

This  disease  is  different  from  crown  gall  or  tuber- 
culosis. Although  the  symptoms  are  sometimes 
manifested  as  knots  or  outgrowths  on  the  main 
roots,  usually  the  knots  are  found  at  the  tip  end 
of  the  roots,  thereby  leaving  unmolested  the  main 
root.  The  effect  of  this  disease,  however,  is  to  re- 
duce the  size  of  the  marketable  beet.  Affected 

9 


130  Diseases  of  Truck  Crops 

plants  in  the  field  may  be  detected  by  their  stunted 
growth,  smallness  and  paleness  of  foliage. 

Cause  and  Control.  The  cause  of  this  trouble  is 
not  a  bacterium  or  a  fungus  but  a  minute  micro- 
scopical worm,  Heterodera  radicicola.  For  further 
description  of  the  parasite  and  for  methods  of  control 
see  p.  49-51. 

DISEASES  OF  SPINACH  (Spinacia  okracea) 

Spinach  is  an  important  truck  crop  in  the  United 
States  but  one  subject  to  numerous  diseases. 

MALNUTRITION 

The  result  of  an  excess  of  acidity  or  of  a  lack  of 
soil  humus. 

This  condition  causes  great  losses  in  those  districts 
where  commercial  fertilizers  are  used  exclusively,  at 
the  expense  of  organic  manures. 

The  margins  of  the  veins  of  the  leaves  become  yellow 
and  the  central  part  takes  on  a  mottled  appearance. 
The  outer  leaves  are  usually  the  first  to  suffer;  soon, 
however,  the  entire  plant  exhibits  similar  symptoms 
and  ceases  to  grow. 

Control.  Spinach,  like  lettuce  and  other  crops 
which  are  eaten  for  their  foliage,  cannot  be  sprayed 
with  poisonous  fungicides.  The  trucker  must  look 
to  other  sources  for  relief.  The  methods  for  control- 
ling malnutrition  have  already  been  considered  on 
pages  81-82.  As  regards  the  other  diseases  men- 


FIG.  21.     SPINACH  DISEASES. 

a.  Downy  mildew,  b.  cross  section  showing  fruiting  stalk  of  the  downy  mildew 
fungus  on  infected  spinach  leaf,  c.  cross  section  showing  leaf  affected  with  white 
smut,  d.  Anthracnose  of  spinach,  e.  cross  section  showing  acervulus  of  Colletolri- 
chum  spinacice,  f.  leaf  spot,  g.  spores  of  the  leaf  spot  fungus  Heterosporium  variabile- 
(b.  c.  e.  after  Halsted,  d.  after  Reed). 


^Family  Chenopodiaceae  131 

tioned  above,  clean  culture  is  an  important  consid- 
eration. Diseased  leaves  should  be  collected  and 
destroyed  by  fire;  the  diseased  refuse  should  never 
find  a  place  in  the  manure  pile.  Where  spinach  has 
been  grown  too  long  on  the  same  land  a  rest  must  be 
given  by  rotating  with  other  crops. 

DOWNY  MILDEW 
Caused  by  Peronospora  effusa  Rabenh. 

The  downy  mildew  of  spinach  is  of  widespread 
occurrence.  The  disease  causes  great  damage  during 
seasons  of  heavy  rainfall  or  during  dry  weather  ac- 
companied by  heavy  dews  at  night.  It  is  rare  in  dry 
weather  and  absence  of  dews. 

Symptoms.  The  trouble  is  characterized  by  yellow 
spots  of  conspicuous  size  on  the  upper  part  of  the 
leaves  (fig.  21  a).  On  the  under  side  of  the  leaves 
and  corresponding  to  the  spots  above,  is  seen  a 
mat  of  dirty  white  to  violet  gray  fruiting  bodies  of 
the  fungus. 

The  Organism.  Downy  mildew  is  caused  by  the  fun- 
gus Peronospora  effusa.  The  spores  of  the  parasite 
are  borne  on  branches  which  generally  emerge  through 
the  breathing  pores  or  stomata  of  the  lower  part 
of  the  leaf  (fig.  21  b)  and  germinate  by  sending  out 
a  slender  germ  tube.  Infection  takes  place  when  the 
germ  tube  penetrates  the  upper  side  of  the  leaf,  gen- 
erally through  the  stomata.  The  winter  stage  or 
oospores  may  be  found  in  the  affected  leaves.  The 


132  Diseases  of  Truck  Crops 

fungus  also  seems  able  to  pass  from  year  to  year  as 
viable  mycelium  in  the  late  infected  leaves  of  the 
spinach. 

ANTHRACNOSE 

Caused  by  Colletotrichum  spinacia  Ell.  and  Hals. 

• 

This  disease  is  apparently  limited  to  New  Jersey 
and  Virginia,  although  it  probably  occurs  also  in 
other  States  where  spinach  is  grown. 

Symptoms.  It  appears  as  minute  round  water- 
soaked  spots  on  the  leaves.  These  quickly  enlarge 
and  become  gray  and  dry  (fig.  21  d).  In  the  spots 
will  be  found  evenly  scattered  minute  dark  tufts; 
these  are  merely  fruiting  pustules  which  also  contain 
minute  black  bristles  or  setae  (fig.  21  e).  The  onset 
is  not  limited  to  any  particular  part  of  the  plant.  In- 
fection may  take  place  anywhere  on  the  foliage, 
stems,  or  petioles.  The  spore  pustules  may  be  formed 
on  the  upper  as  well  as  on  the  lower  surface  of  the 
leaf.  In  wet  moist  weather  the  pustules  take  on  a 
salmon  tinge,  indicating  that  there  is  an  abundance  of 
spores  formed  at  that  time.  The  spores  may  be 
carried  from  leaf  to  leaf  and  from  plant  to  plant  by 
insects,  wind,  or  rainwater.  In  badly  infected  fields, 
picking  should  never  be  done  during  wet  rainy 
weather,  neither  should  spinach  from  infected  fields 
be  allowed  to  be  shipped  long  distances,  as  in  this 
case  the  product  may  rot  before  reaching  its  destina- 
tion. 


Family  Chenopodiaceae  133 

WHITE  SMUT 
Caused  by  Entyloma  Ellisii  Hals. 

Spinach  smut  is  closely  related  to  the  smut  of 
onions  or  even  to  the  grain  smuts.  The  disease  is  of 
rare  occurrence. 

Symptoms.  Instead  of  turning  black,  the  leaves 
assume  a  white  frosty  appearance,  which  renders 
them,  of  course,  worthless.  The  fungus  has  two  forms 
of  spores.  Those  within  the  leaf  are  spherical  and 
grouped  in  small  clusters  just  beneath  the  stomata, 
while  the  second  form  is  needleshaped  and  is  borne 
at  the  end  of  the  minute  threads  on  the  surface  of  the 
affected  leaf  (fig.  21  c). 

PHYLLOSTICTA  LEAF  BLIGHT 
Caused  by  Phyllosticta  chenopodii  Sacc. 

This  is  a  common  disease,  especially  with  older 
plants.  Like  Anthracnose,  leaf  blight  causes  great 
damage  when  once  introduced  in  a  field. 

Symptoms.  Numerous  minute  spots  appear,  more 
distinctly  in  the  lower  part  of  the  leaf.  Within  them 
are  found  scattered  minute  black  bodies  known  as 
pycnidia.  These  are  microscopical,  saclike  bodies, 
within  which  the  spores  of  the  fungus  are  borne. 
During  moist  weather,  the  spores  are  seen  to  ooze 
out  as  long  white  tendrils.  The  latter  are  made  up 
of  millions  of  spores  held  together  by  a  mucilaginous 


134  Diseases  of  Truck  Crops 

substance  which  is  dissolved  by  the  least  contact 
with  rainwater  or  dew.  The  spores  are  then  carried 
about  by  the  same  agencies  as  mentioned  for  the  or- 
ganism of  spinach  anthracnose. 

BLACK  MOLD 
Caused  by  Cladosporium  macrocarpum  Preuss. 

This  disease  attacks  the  oldest  leaves  of  the  plant 
in  dark  patches  which  are  covered  with  numerous  ir- 
regular dark  spore-bearing  branches  or  conidiophores. 
It  is  of  little  economic  importance. 

LEAF  SPOT 
Caused  by  Heterosporium  variabile  Cke. 

This  disease  is  very  prevalent  on  winter  spinach 
in  Eastern  Virginia.  It  generally  attacks  plants 
which  have  been  weakened  by  downy  mildew,  or  by 
other  diseases.  Reed  and  Cooley, z  who  have  studied 
it  carefully,  find  that  indirectly  it  causes  considerable 
losses  to  the  growers.  It  necessitates,  for  instance, 
the  trimming  off  of  dead  or  diseased  leaves,  this 
requiring  extra  labor  and  reducing  the  quantity  of 
marketable  spinach.  The  disease  is  at  its  height 
when  the  plants  attain  their  maximum,  beginning  in 
January  and  continuing  until  about  March,  the  close 

1  Reed,  H.  L.,  and  Cooley,  J.  S.,  Virginia  Agr.  Expt.  Sta.  Ann. 
Rept.  1909  and  1910. 


Family  Chenopodiaceae  135 

of  the  season.  Leaf  spot  does  not  develop  to  any 
appreciable  extent  under  dry  conditions.  In  dry 
winters  it  is  of  no  economic  importance.  It  is  best 
favored  by  poor  soil  conditions,  that  is  by  an  excess 
of  acidity  or  a  lack  of  humus. 

The  Organism.  It  is  caused  by  Heterosporium 
var labile,  a  semi-parasitic  fungus  which  causes  circu- 
lar, or  subcircular,  sooty  brown  spots,  having  a 
definite  outline  (fig.  21  f)  on  both  sides  of  the  leaf, 
surrounded  by  a  brown  area  of  dead  leaf  tissue. 
The  spots  at  first  have  a  light  color,  becoming  darker 
with  age,  finally  turning  velvety  to  olive  black.  This 
color  is  largely  due  to  the  appearance  of  the  spores 
on  the  surface  of  the  spots.  These  occur  singly, 
although  they  may  involve  the  entire  leaf  when  a 
great  number  coalesce.  The  mycelium  grows  in  the 
host  cells  and  consists  of  septate  branches,  the  cells  of 
which  are  olive  green  in  color,  irregular  in  shape, 
granular  and  oily  in  content.  Conidiophores  pro- 
ceed vertically  from  cracks  in  the  epidermis  of  the 
spot,  and  at  the  tip  end  of  each  a  spore  is  borne  on  a 
small  short  pedicel.  As  the  conidiophore  continues  in 
growth,  new  spores  are  formed  at  the  tip  end,  thus 
giving  the  fruiting  stalk  a  twisted  appearance.  The 
mature  spore  is  three  celled  (fig.  21  g),  cylindrical, 
with  round  or  slightly  pointed  ends,  spiny,  and  sooty 
or  olive  green  in  color.  On  pure  culture  the  fungus 
may  produce  only  one-celled  spores.  The  latter 
seem  to  retain  their  vitality  for  at  least  six  months. 

The  very  serious  spinach  blight  of  the  Norfolk, 
Va.,  trucking  region  should  be  mentioned.  It  was 


136  Diseases  of  Truck  Crops 

erroneously  confused  by  Harter  with  the  true  mal- 
nutrition which  is  also  found  there  (but  rather  rarely) . 
The  blight  has  been  shown  by  McClintock  and  Smith 
to  be  a  true  mosaic,  communicated  by  aphids.  ' 

WEEDS 

"  Disease  is  not  confined  to  cultivated  crops  only, 
but  it  also  attacks  weeds.  In  attempting  to  control 
the  diseases  of  cultivated  crops,  we  cannot  lose  sight 
of  the  various  weed  pests  of  the  truck  garden,  inas- 
much as  they  are  liable  to  several  important  diseases 
in  common  with  the  cultivated  crops.  Clean  culture 
tends  to  destroy  those  weeds  which  act  as  carriers  of 
some  of  these  diseases.  The  more  important  weeds 
in  this  family  are  lamb's-quarters  (Chenopodium 
album),  the  wormseed  (Chenopodium  anthelminticum) , 
orache  (Ar triplex  patula),  and  Russian  thistle  (Salsola 
tragus,  Salsola  kali,  and  Salsola  pestifer).  As  far  as 
we  know,  none  of  the  diseases  which  attack  beets  are 
known  to  prey  on  these  weeds.  However,  the  downy 
mildew  of  spinach,  Peronospom  effusa,  attacks  also 
the  lamb's-quarters,  the  worm  seed,  and  the  orache. 
From  this  fact  may  be  seen  the  importance  of  clean 
culture  in  the  control  of  downy  mildew.  In  trucking, 
as  in  every  system  of  intensive  culture,  weeds  are  sel- 
dom tolerated.  But  they  are  often  overlooked  on  the 
roadside  and  around  old  fences,  where  they  cause 
clean  culture  to  be  of  no  avail.  Weeds  should 
never  be  tolerated  anywhere  within  the  reach  of  the 
trucker  or  gardener. 


CHAPTER  XI 

FAMILY  COMPOSITE 

THIS  important  family  includes  the  artichoke 
(globe  and  Jerusalem),  chicory,  endive,  lettuce,  salsi- 
fy, and  sunflower.  As  far  as  we  know,  there  are  no 
available  statistics  of  the  acreage  and  money  value  in 
the  United  States  of  artichoke,  chicory,  salsify,  and 
sunflower.  They  are,  nevertheless,  of  considerable 
economic  importance.  According  to  the  Thirteenth 
Census  of  the  United  States  (1909)  the  area  in  lettuce 
was  5489  acres,  and  the  crop  is  estimated  at  $1,595- 
085.  Florida  leads  with  1450  acres  and  New  York 
follows  with  1012  acres.  The  other  States  in  order 
of  importance  are  California,  Louisiana,  Massachu- 
setts, Illinois,  New  Jersey,  Missouri,  Pennsylvania, 
Ohio,  Virginia,  and  Maryland.  States  with  less  than 
100  acres  of  lettuce  are  omitted. 

DISEASES  OF  ARTICHOKE,  JERUSALEM 
(Helianthus  tuberosus) 

Jerusalem  artichoke  is  subject  to  the  attack  of  but 
few  diseases.  With  the  exception  of  downy  mildew, 
none  needs  to  be  feared  by  the  trucker  or  gardener. 

137 


138  Diseases  of  Truck  Crops 

DOWNY  MILDEW 
Caused  by  Plasmopara  Halstedii  (Farl.)  B.  and  D. 

This  mildew  attacks  the  Jerusalem  artichoke  as 
well  as  the  sunflower.  The  disease  is  of  little  eco- 
nomic importance.  The  trouble  is  apparent  as 
downy  whitish  patches  on  the  under  side  of  the  leaves 
which  soon  spread,  involving  the  entire  area  of  the 
affected  foliage.  This  soon  turns  yellowish,  becomes 
dry  and  brittle,  and  dies. 

RUST 

Caused  by  Puccinia  helianthi  Schw. 

This  rust  is  supposed  to  be  the  same  as  the  rust  of 
the  sunflower.  However,  the  work  of  Arthur1  shows 
that  no  infection  takes  place  when  the  teliospores 
from  the  sunflower  are  sown  on  the  Jerusalem  arti- 
choke. It  is  probable  that  we  deal  with  physiological 
races.  The  rust  on  the  artichoke  is  characterized 
by  numerous  spore  pimples,  yellow  at  first  but  later 
turning  to  dark  brown. 

LEAF  BLOTCH 
Caused  by  Ramularia  cynarcz  Sacc. 

This  disease  has  as  yet  proved  to  be  of  little 
economic  importance  in  the  United  States.  In 
Europe,  however,  leaf  blotch  seems  to  cause  con- 

1  Arthur,  J.  C.,  Mycologia,  11  153,  1905. 


Family  Composite  139 

siderable  damage.  Grayish  irregular  spots  appear 
on  the  leaves  and  often  become  so  numerous  as  to 
involve  the  entire  surface,  in  which  case  the  affected 
leaf  becomes  brown  and  eventually  dies. 

DISEASE  OF  ARTICHOKE,  GLOBE  (Cynara 
scolymus) 

The  globe  artichoke  is  little  cultivated  and  very 
little  known  to  the  people  of  the  United  States.  In 
Europe  and  especially  in  Asia  this  delicious  truck 
crop  is  more  extensively  grown.  Globe  artichoke  is, 
as  far  as  known,  attacked  by  few  diseases. 

LEAF  SPOT" 
Caused  by  Cercospora  obscura  H.  and  W. 

Heald  and  Wolf1  found  this  disease  on  the  globe 
artichoke  in  Beeville,  Texas.  The  disease  is  char- 
acterized by  minute  gray  spots  on  the  upper  surface 
of  the  leaf.  The  gray  color  is  brought  about  by  the 
appearance  of  the  tufts  of  conidiophores  and  conidia 
on  the  surface  of  the  spots. 

The  conidiophores  of  the  fungus  are  non -sept ate, 
borne  in  groups  of  four  to  seven,  and  hyaline  at  the 
tips.  The  conidia  are  cylindrical  in  shape,  straight 
or  curved. 

Control.  None  of  the  diseases  of  the  Jerusalem  or 
the  globe  artichoke  are  ever  serious  enough  to  attract 
attention.  However,  where  these  crops  are  grown 

1  Heald,  F.  D.,  and  Wolf,  F.  A.,  Mycologia,  3  :  5-22,  1911. 


140  Diseases  of  Truck  Crops 

extensively,  spraying  with  Bordeaux  4-4-50  is  re- 
commended for  downy  mildew  (Plasmopara  Halstedii) 
of  the  Jerusalem  artichoke,  and  for  leaf  blotch  (Ramu- 
laria  cynarcz) .  In  damp  weather  it  may  be  necessary 
to  spray  from  three  to  four  times  during  the  season. 

DISEASES  OF  LETTUCE  (Lactuca  saliva) 

Lettuce  is  subject  to  numerous  diseases  in  the  field 
on  account  of  the  extreme  tenderness  of  the  foliage. 
None  of  the  diseases  to  be  mentioned  should  be 
allowed  to  gain  a  foothold  in  the  fields. 

BACTERIAL  BLIGHT 
Caused  by  Pseudomonas  viridilividum  Br. 

This  is  a  serious  disease,  common  especially  in 
Louisiana  and  in  other  States  where  lettuce  is  grown 
extensively.  The,  disease  was  first  described  by 
Brown1  who  found  that  large  acreages  of  lettuce  were 
ruined  by  the  blight.  The  growers  at  first  believed 
that  the  trouble  was  brought  about  by  the  use  of 
cottonseed  meal.  However,  this  was  proven  to  be 
not  true,  since  the  trouble  was  also  found  to  a  very 
serious  extent  where  no  cottonseed  meal  was  used  as 
a  fertilizer.  The  writer  has  found  the  same  trouble 
in  the  lettuce  fields  in  Texas. 

Symptoms.     The  disease  seems  to  attack  only  the 

1  Brown,  Nellie  A.,  U.  S.  Dept.  of  Agr.  Jour.  Agr.  Research,  4  : 
417-478,  1915.  ,,:>- 


Family  Composite  141 

outer  leaves  of  a  head.  The  affected  foliage  is  first 
covered  with  numerous  watersoaked  spots  which 
enlarge,  fuse  together,  and  involve  the  entire  area  of 
the  affected  leaves.  The  latter  either  soften  or  dry 
up,  opening  up  the  way  for  the  entrance  of  other 
decay  organisms,  which  may  now  attack  the  other- 
wise sound  head. 

The  organism  is  rod-shaped,  occurring  singly  or 
in  pairs,  or  in  chains,  and  it  moves  about  by  means 
of  polar  flagella.  On  agar,  the  young  colonies  are 
round  with  entire  smooth  margins;  they  are  trans- 
lucent cream  white  in  reflected  light  but  bluish  in 
transmitted  light.  The  older  colonies  are  not  always 
uniform  in  color,  but  may  take  on  yellowish  bands 
or  become  mottled.  The  organism  does  not  form  gas 
and  it  liquefies  gelatine  slowly.  It  is  not  especially 
sensitive  to  sunlight. 

Control.  It  is  not  as  yet  known  whether  Bordeaux 
mixture  will  control  the  disease.  The  disease  should 
not  be  allowed  to  gain  any  headway  in  the  field. 
Diseased  plants  should  not  be  fed  to  cattle  nor  al- 
lowed to  find  a  place  in  the  manure  pile,  but  should 
be  destroyed  by  fire.  In  severely  affected  fields  other 
crops  should  be  grown  and  the  land  be  given  a  rest 
from  lettuce  for  at  least  three  years. 

DOWNY  MILDEW 
Caused  by  Bremia  lactucce  Reg. 

Downy  mildew  is  a  disease  which  is  more  trouble- 
some in  Europe  than  in  the  United  States,  and  it  is 


Diseases  of  Truck  Crops 

more  serious  on  greenhouse  lettuce  than  on  that 
grown  in  the  open.  In  the  field  it  usually  attacks  fall 
lettuce. 

Symptoms.  Affected  leaves  lose  their  natural 
green  color  and  turn  yellow.  A  careful  examination 
will  disclose  a  delicate  downy  web  on  the  under  side 
of  the  foliage  which  will  have  a  wilted  appearance. 
The  downy  web  consists  of  the  conidiophores  of  the 
fungus.  These  appear  singly  and  are  much  branched. 
The  conidia  germinate  by  means  of  a  germ  tube. 
Downy  mildew  attacks  not  Only  lettuce,  but  also  chic- 
ory and  numerous  other  Composite. 

Control.  Spraying  lettuce  is  not  recommended. 
Clean  culture  and  careful  regulation  of  the  soil  mois- 
ture will  help  to  control  this  trouble.  Downy 
mildew  is  seldom  found  on  well  drained  lands.  In 
greenhouses,  the  disease  may  be  checked  by  the 
sudden  lowering  of  temperature  for  a  day  or  two. 
Soil  sterilization  with  formaldehyde  (see  p.  53)  will 
also  be  effective. 

GRAY  MOLD 
Caused  by  Sclerotinia  Fuckeliana  De  Bary 

Gray  mold  attacks  grapes  in  Europe  but  in  the 
United  States  it  is  commonly  met  with  in  the  lettuce 
fields,  especially  on  plants  which  are  fully  developed 
and  somewhat  overgrown. 

Symptoms.  The  disease  is  manifested  by  soft, 
watersoaked  spots  on  the  foliage  causing  a  wilting. 
The  spots  soon  become  coated  with  the  fruit  of  a 


FIG.  22.     LETTUCE  DROP. 

To  the  right,  artificially  inoculated  plant;  to  the  left,  healthy. 


Family  Composite  143 

gray  mold.  The  fungus  has  two  stages.  Botrytis 
cinerea  Pers.  of  wilted  lettuce  leaves  appears  as  a 
gray  mold,  the  other  is  the  winter  or  apothecial  stage. 
American  botanists  have  not  as  yet  been  able  to  con- 
nect these  two  forms.  It  seems,  however,  that 
Istvanffi1  was  able  to  confirm  the  work  of  De  Bary, 
who  first  indicated  the  relationshp  of  Botrytis  cinerea 
with  Sclerotinia  Fuckeliana. 

LETTUCE  DROP 
Caused  by  Sclerotinia  libertiana  Fckl. 

Drop  is  a  disease  which  is  found  wherever  lettuce 
is  grown.  The  greatest  damage  is  reported  from  the 
South  Atlantic  States,  North  and  South  Carolina, 
Alabama,  Georgia,  Florida,  Louisiana,  although  the 
trouble  extends  also  to  such  States  as  Massachusetts, 
New  York,  Ohio,  Pennsylvania,  Connecticut,  Rhode 
Island,  Wisconsin,  Iowa,  Washington,  Vermont, 
Maine,  Maryland,  Delaware,  and  Virginia. 

Symptoms.  The  term  drop  best  describes  the 
symptoms  of  the  disease.  The  first  sign  is  a  wilting 
of  the  lower  leaves  (fig.  22),  which  is  immediately 
followed  by  a  drooping  of  upper  ones  until  the  entire 
plant  is  involved.  The  affected  plant  has  a  sunken 
appearance  as  if  scalded  with  boiling  water.  In 
examining  a  dead  plant,  a  white  cottony  fungus 
growth  is  found  on  the  under  side  of  the  lower  leaves, 
and  near  the  moist  regions  at  the  stem  end. 

1  Istvanffi,  G.  De,  Ann.  de  1'institut  central  ampel.  roy.  Hongnois: 
183-360,  1915. 


144         .  Diseases  of  Truck  Crops 

When  the  plants  are  fairly  rotted,  there  appear  on 
the  cottony  mycelial  growth  mentioned  above,  black 
bodies,  or  sclerotia,  which  vary  in  size  from  a  pin- 
head  to  a  grain  of  corn.  The  three  definite  symptoms 
of  the  disease  may  be  summarized:  (i)  drooping,  (2) 
cottony-like  mycelial  growth  on  the  under  surface  of 
the  affected  leaves,  (3)  the  appearance  of  sclerotia 
(fig.  23  c).  The  latter  help  to  carry  over  the  fungus 
during  the  winter.  After  the  sclerotia  have  been  in 
the  soil  over  winter,  they  germinate  in  the  following 
spring  by  sending  out  small  mushroom-like  fruiting 
bodies  known  as  apothecia  (fig.  23  a).  The  latter 
contain  small  sacs  or  asci  which  bear  the  spores  (fig. 
23  b  and  d). 

Control.  The  work  of  Stevens r  seems  to  show  that 
lettuce  drop  may  be  controlled  by  the  following 
method:  The  field  is  inspected  as  often  as  possible 
during  the  season.  Every  plant  which  shows  indica- 
tions of  disease  is  pulled  out  and  burned  and  the 
place  where  it  grew  is  drenched  with  a  solution  of  one 
pound  of  bluestone  dissolved  in  seven  gallons  of  water. 
If  these  directions  are  carried  out  for  three  years  the 
disease  will  be  controlled.  The  simplicity  of  the 
method  should  make  it  appeal  to  truckers  and  gar- 
deners. 

LEAF  SPOT 

Caused  by  Septoria   lactuccz   Pass,   and   Septoria 
consimilis  E.  and  M. 

1  Stevens,  F.  L.,  North  Carolina  Agr.  Expt.  Sta.  Bui.  217  : 7-21, 
1917. 


FIG.  23.     LETTUCE  DISEASES. 

a  Germinating  sclerotium  of  Sclerotinia  libertiana 
the 'cause  of  lettuce  drop,  b.  section  of  fruiting  cup 
(apothecium)  showing  asci,  ascospores  and  parapnyses 
of  S.  libertiana,  c.  section  through  sclerotium  of  A. 
libertiana,  d.  germinating  ascospore  of  .S  .libertiana  (a. 
to  d.  after  F.  S.  Stevens),  e.  Cercospora  leaf  spot. 


Family  Composite  145 

This  disease  is  induced  by  two  species  of  Septoria 
fungi.  The  symptoms  produced  by  both  are  -so 
nearly  alike  that  it  is  difficult  to  distinguish  one  from 
the  other,  except  by  microscopic  examination.  Pale 
brown  discolored  spots  appear  on  the  older  leaves 
with  numerous  black  pycnidia  in  the  center.  The 
disease  is  of  little  economic  importance,  as  it  usually 
occurs  late  in  the  season,  on  plants  which  have  nearly 
passed  their  usefulness.  The  Boston  variety  is  con- 
sidered resistant,  while  the  Salamander  and  the 
Wonderful  are  more  susceptible  to  leaf  spot. 

SHOT  HOLE 
Caused  by  Marsonia  perforans  E.  and  E. 

The  disease  is  of  little  economic  importance.  Af- 
fected leaves  are  covered'  with  dry  spots  which  drop 
out,  leaving  irregular  perforations.  Along  the  border 
of  these  holes,  the  causative  fungus  may  be  found 
abundantly  fruiting.  The  disease  attacks  the  mid- 
ribs of  the  leaves  as  well  as  the  stem  of  the  plants. 
It  seems  to  be  more  prevalent  under  conditions  of 
surface  irrigation.  With  sub-irrigation,  on  the  other 
hand,  it  is  not  found  to  cause  any  damage. 

CERCOSPORA  LEAF  SPOT 
Caused  by  Cercospora  lactucce  Stev. 

This  disease  is  as  yet  of  no  importance  in  the 
United  States.  The  trouble  occurs  in  Porto  Rico, 

10 


146  Diseases  of  Truck  Crops 

where  it  has  been  recently  described  by  Stevenson. x 
The  causative  fungus  attacks  the  older  and  lower 
leaves,  forming  numerous  irregular,  ragged  spots 
(fig.  23  e). 

ROSETTE,  see  Rhizoctonia,  p.  45 

ROOT  KNOT 
Caused  by  Heterodera  radicicola  (Greef)  Muller. 

This  disease  is  prevalent  in  the  light  sandy  loams 
which  are  infected  with  eelworm.  Small,  stringy, 
bead-shaped  knots  form  on  the  roots  and  rootlets. 
Lettuce  thus  affected  seldom  succeeds  in  heading  out, 
but  remains  dwarfed  and  sickly  looking.  For  a 
further  description  of  the  trouble  and  its  control 
see  p.  49. 

DISEASES  OF  SALSIFY  (Tragopogon 
porrtfolius) 

Salsify,  or  oyster  plant  as  it  is  commonly  known,  is 
subject  to  but  few  diseases,  all  of  which  are  generally 
of  little  economic  importance.  This  is  perhaps  due 
to  the  fact  that  it  is  little  grown  and  that  its  edible 
qualities  are  little  appreciated  by  the  American 
consumer. 

SOFT  ROT 
Caused  by  Bacillus  carotovorus  Jones 

1  Stevenson,  J.  A.,  Journal  Department  of  Porto  Rico,  I  :  93- 
117,  1917. 


Family  Composites  147 

Soft  rot  of  salsify  is  more  a  storage  trouble  than  a 
field  trouble.  The  disease,  as  it  has  been  studied  by 
Clinton, T  was  found  to  be  the  same  as  the  soft  rot  of 
the  carrot  and  of  various  other  vegetables.  It  was 
found  in  salsify  roots  stored  in  poor  cellars,  lacking 
the  necessary  ventilation. 

Symptoms.  Soft  rot  usually  begins  at  the  crown 
and  works  downwards  into  the  heart  of  the  root. 
The  outside  and  harder  tissue  remains  sound  and 
seems  to  form  a  firm  coating  to  the  centrally  decayed 
tissue.  The  bacteria  work  first  in  the  fibro-vascular 
bundles,  the  soft  rotted  portion  being  found  in  the 
center  of  the  root.  The  germ  Bacillus  carotovorus, 
the  cause  of  the  soft  rot  of  carrots,  is  responsible  also 
for  this  disease  of  the  salsify. 

Control.  It  is  suggested  that  roots  which  show  soft 
rot  should  not  be  used  for  seed  crops.  Diseased 
roots  should  not  be  fed  to  cattle  nor  should  they  be 
dumped  on  the  manure  pile.  The  storage  cellar 
should  be  allowed  plenty  of  ventilation,  especially 
during  the  first  three  weeks  of  storage. 

WHITE  RUST 
Caused  by  Albugo  tragopogonis  (D.  C.)  Gray. 

White  rust  is  a  field  disease  that  seldom  gives  any 
trouble  in  dry  seasons,  nor  is  it  found  to  any  appre- 
ciable extent  on  new  lands.  The  disease  is  charac- 

1  Clinton,  G.  P.,  Connecticut  Agr.  Expt.  Sta.,  38th,  Ann.  Rept, ; 
25-27,  1914. 


148  Diseases  of  Truck  Crops 

terized  by  whitish  blisters  or  sori  on  the  leaves. 
When  these  blisters  are  mature,  they  burst  open,  liber- 
ating a  white  dust  composed  of  the  spores  of  the  para- 
site. In  badly  infected  plants  diseased  leaves  turn 
black  and  split  and  tear  lengthwise.  The  rust  at- 
tacks leaves  only,  resulting  indirectly  in  small  and 
dwarfed  roots.  To  keep  this  trouble  in  check  salsify 
should  be  planted  on  new  land. 

RUST 

Caused  by  Puccinia  tragopogoni  (Pers.)  Cda. 

This  rust  resembles  the  white  rust  in  appearance, 
except  that  the  blisters  here  are  brown  instead  of 
white.  It  is  found  wherever  salsify  is  grown,  but  it 
does  not  seem  to  have  caused  considerable  damage. 
The  life  history  of  the  fungus  is  little  known. 

SOUTHERN  BLIGHT  (FIG.  24),  see  PEPPER,  p.  305 

DISEASES  OF  THE  SUNFLOWER 
(Helianihus  annuus) 

The  sunflower  can  hardly  be  considered  a  truck 
crop.  Nevertheless,  this  plant  finds  a  place  in  truck- 
ing, as  it  is  often  grown  for  its  seed  as  a  poultry 
feed.  Sunflower  seedlings  are  subject  to  damping 
off,  Pythium  de  Baryanum  Hesse.  For  a  detailed 
description  of  this  trouble,  see  pages  42-44. 

DOWNY  MILDEW  (Plasmopora  Halstedii  Farl.) 
of  the  sunflower  is  not  different  from  the  same  dis- 
ease on  Jerusalem  artichoke,  p.  138.  v 


FIG.  24.     SOUTHERN  BLIGHT  OF  THE  SALSIFY. 

the  right  healthy  plant,  to  the  left  diseased  plant,  with  root  rotted  off. 


Family  Composite  149 

RUST 

Caused  by  Puccinia  helianthi  Schw. 

Rust  attacks  the  wild  as  well  as  the  cultivated  sun- 
flower, producing  blisters  or  sori  on  the  leaves.  The 
former  are  at  first  yellow  or  brown,  but  later  in  the 
season  become  black.  Badly  infected  leaves  turn 
yellow,  then  curl  and  dry  up.  This  results  in  a  re- 
duction in  the  yield  of  seed,  which  for  the  most  part 
fails  to  fill  out  properly.  This  rust  seems  to  attack 
the  sunflower  only  and  is  apparently  unable  to  infect 
the  Jerusalem  artichoke.  Clean  culture  and  des- 
troying the  refuse  by  fire  is  advised. 

WEEDS 

The  family  Composite  contains  a  large  number  of 
weeds.  The  following  are  often  troublesome:  rag- 
weed (Ambrosia  artemisifolia),  great  ragweed  (Am- 
brosia trifida),  Mayweed  (Anthemis  cotula),  burdock 
(Arctium  minus),  ox-eye  daisy  (Chrysanthemum 
leucanthemum  pinnatifidum) ,  blue  sailors  (Cicorum 
intybus),  bull  thistle  (Cirsium  lanceolatum) ,  fireweed 
(Erechtites  hieracifolia) ,  wild  or  tall  lettuce  (lactuca 
canadensis),  prickly  lettuce  (Lactuca  scariola),  fall 
dandelion  (Leontodon  autumnalis),  Canada  golden- 
rod  (Solidago  canadensis) ,  dandelion  (Taraxacum 
qfficinale),  cocklebur  (Xanthium  commune). 

Of  the  weeds  which  are  attacked  by  downy  mildew, 
Plasmopara  Halstedii  Farl.,  may  be  mentioned  the 
ragweed,  the  great  ragweed,  and  Canada  goldenrod. 


150  Diseases  of  Truck  Crops 

None  of  the  weeds  here  mentioned  is  attacked  by 
rust,  Puccinia  helianthi  Schw.  If  downy  mildew  is  to 
be  kept  in  check  the  truck  patches  must  be  kept  free 
from  weeds. 


CHAPTER  XII 

FAMILY    CONVOLVULACE/E 

THIS  important  family  includes  but  one  truck 
crop,  the  sweet  potato.  The  latter  is  of  great  eco- 
nomic importance  to  truckers  who  are  situated  in 
sandy  or  sandy  loam  regions.  Sweet  potatoes  cannot 
thrive  in  heavy  clay  soils. 

According  to  the  Thirteenth  Census  of  the  United 
States,  the  total  acreage  of  sweet  potatoes  in  1909 
was  641,255  acres,  with  a  total  production  of  52,232,- 
070  bushels,  worth  $35,429,176.  North  Carolina 
has  the  distinction  of  having  the  largest  acreage  in 
sweet  potatoes,  84,740.  The  other  States  which 
follow,  according  to  rank,  are,  Georgia,  Alabama, 
Louisiana,  Mississippi,  South  Carolina,  Texas,  Vir- 
ginia, Tennessee,  New  Jersey,  Arkansas,  Florida, 
Kentucky,  Illinois,  Maryland,  Missouri,  Delaware, 
Oklahoma,  Kansas,  Iowa,  and  West  Virginia.  States 
with  less  than  2000  acres  are  here  omitted. 

DISEASES  OF  THE   SWEET  POTATO 
(Convolvulus  batatas) 

Sweet  potatoes  are  subject  to  numerous  field  and 
storage  diseases,  many  of  which  may  be  controlled. 


152  Diseases  of  Truck  Crops 

SLIME  MOLD 

Caused  by   Fuligo  molacea  Pers.  and  Physarum 
plumbeum  Fries. 

Very  often  the  plants  in  the  seed  beds  are  covered 
with  white,  yellowish,  or  purple  jellylike  growths. 
These  patches  may  vary  from  three  to  six  inches  or 
more  in  diameter  and  cover  the  foliage,  peduncles, 
and  stems.  In  12  to  24  hours  this  slime  thickens  and 
becomes  covered  with  a  white  or  yellowish  crust 
which  readily  cracks  and  liberates  the  spores  in  the 
form  of  a  dark  brown  powder.  The  growth,  which 
is  a  slime  mold,  .has  been  determined  as  Fuligo 
molacea  Pers.  (fig.  25  a).  The  organism  is  not  a 
parasite  on  the  sweet  potato  plant;  nevertheless  its 
presence  in  a  seed  bed  is  not  desirable.  The  slime 
mold  covers  the  plant,  shutting  off  light  which  is  es- 
sential for  its  proper  nutrition.  There  is  another 
slime  mold,  Physarum  plumbeum  Fries.,  which  often 
grows  on  the  foliage  (fig.  25  b).  These  molds  are 
seen  only  in  seed  beds  in  the  open  or  on  sweet  potato 
beds  in  the  greenhouse. 

"SOIL  ROT,"  "Pox,"  OR  "PIT" 
Caused  by  Cystospora  batatas  E. 

The  term  soil  rot  is  somewhat  misleading,  as  the 
disease  does  not  produce  a  rot.  The  name  "pox" 
or  "pit"  is  a  better  description  of  the  disease. 


FIG.  25.     SWEET  POTATO  DISEASES. 

a.  Slime  mold  (Fuligo  violaced),  b.  slime  mold  (Physarum  plumbeum),  c.  pox  or 
pit,  d.  formation  of  a  cyst  and  liberation  of  spores  of  Cystospora  batata  (after  Elliot), 
e.  white  rust,  /.  oospore  of  the  white  rust  fungus,  g.  soft  rot,  h.  ring  rot,  i.  fruiting 
stalks  of  Rhizopus  nigricans. 


Family  Convolvulaceae  153 

Symptoms.  This  disease  is  early  marked  by 
small,  dark,  dry  spots  on  the  surface  of  the  potato 
(fig.  25  c).  Later  the  infected  portion  in  most  cases 
cracks,  dries,  and  falls  out,  leaving  a  pit  with  a  newly 
formed,  roughened  skin.  It  is  an  underground  trou- 
ble and  is  not  detected  in  the  field  until  late  in  the 
season,  at  a  time  when  healthy  hills  have  formed  well 
developed  vines.  At  this  time  the  lack  of  an  abun- 
dant vine  growth  is  a  characteristic  symptom,  and  the 
rather  meager  stem  development  gives  the  impression 
that  the  soil  is  very  poor  and  exhausted  in  plant  food. 
The  symptom  appears  when  the  sweet  potato  is  begin- 
ning to  form.  At  this  stage  the  spotted  portion 
ceases  to  grow,  while  the  healthy  portion  on  each  side 
continues  to  develop.  Frequently  roots  that  are 
very  badly  spotted  cease  to  grow  altogether,  and  if 
they  are  stored,  the  spots  usually  dry  and  fall  out. 
Unlike  black  rot,  roots  affected  with  soil  rot  do  not 
lose  their  food  value,  as  the  disease  is  only  skin  deep 
and  imparts  no  bad  taste  to  the  potato.  The  disease 
also  attacks  the  young  rootlets  of  the  plant,  and  when 
this  is  the  case  there  is  practically  no  crop  formed. 
This,  however,  happens  only  in  badly  diseased  fields, 
and  especially  where  lime  is  used.  The  latter  should 
never  be  applied  to  lands  infected  with  the  pox  organ- 
ism. The  trouble,  unlike  many  others,  seems  to  be 
worse  in  dry  weather. 

Besides  affecting  the  sweet  potato,  pox  also  causes 
circular  shallow  pits  on  the  white  potato,  and  on 
turnips,  the  pits  on  the  latter  being  even  more  shal- 
low than  on  the  former.  It  is  also  suspected  of  at- 


154  Diseases  of  Truck  Crops 

tacking  beet  and  tomato  plants,  although  complete 
proof  is  still  wanting. 

The  Organism.  The  cause  of  pox  was  first  thought 
to  be  the  fungus  Acrocystis  batatas  E.  and  H.  In- 
vestigations of  the  writer  showed  that  this  was  not 
the  case.  Finally  Elliot I  found  that  pox  was  caused 
by  a  slime  mold  organism  which  he  named  Cysto- 
spora  batatas  E. 

The  swarm  spores  of  the  slime  mold  are  very 
small,  round,  but  slightly  pointed  at  both  ends. 
They  often  fuse  in  pairs,  forming  spherical  bodies 
with  a  single  nucleus.  The  amoebae  soon  become 
circular,  and  four  central  nuclei  together  with  a  dis- 
tinct wall  membrane  become  apparent.  Nuclear 
division  takes  place  and  many  nuclei  are  now  formed 
within  the  cyst  body.  As  the  cyst  advances  in  age, 
a  cell  wall  is  laid  down,  and  each  nucleus  with  its 
surrounding  protoplasm  now  begins  to  round  up  into 
individual  spores.  The  latter  when  mature  break 
through  the  wall  of  the  cyst,  which  dissolves  ap- 
parently through  the  secretion  of  an  enzyme  within 
(fig.  25  d). 

It  is  very  doubtful  if  the  organism  is  carried  with 
infected  sweet  potatoes,  since  the  spots  nearly  always 
dry  and  fall  out.  The  organism  is  carried  over  in 
the  land  from  year  to  year.  The  exact  means  by 
which  it  is  carried  from  place  to  place  is  not  definitely 
known.  The  organism  does  not  seem  to  spread  very 
rapidly  to  adjoining  neighboring  fields,  nor  to  places 
on  the  same  farm. 

1  Elliot,  J.  A.,  Delaware  Agr.  Expt.  Sta.  Bui.  114  :  3-25,  1916. 


Family  Convolvulaceae  155 

WHITE  RUST 
Caused  by  Cystopus  ipomcece-pandMaruz  Farl. 

White  rust  is  a  disease  of  the  foliage  only.  It  is 
present  in  nearly  every  field  where  sweet  potatoes  are 
grown.  Although  prevalent,  the  disease  is  almost 
unrecognized  as  such  by  the  growers.  The  losses 
from  it  are  indirect.  While  it  is  true  that  the  sweet 
potato  is  grown  only  for  its  roots,  nevertheless,  a  good 
crop  depends  upon  a  healthy  and  abundant  stand  of 
leaves.  The  sugar  and  the  starch  in  the  potato  are 
not  manufactured  from  the  soil,  but  are  made  by  the 
leaves  from  the  air  and  sunlight,  and  are  then  stored 
in  the  roots.  The  effect  of  white  rust  is  to  kill  much 
of  the  foliage,  thereby  curtailing  the  amount  of  sugar 
and  starch  manufactured,  and  this  in  turn  results  in  a 
shorter  crop  and  poorer  keeping  roots.  It  is  gener- 
ally agreed  that  the  more  starch  a  root  has,  the  better 
it  keeps.  The  White  Southern  Queen  variety  is  one 
of  the  best  keepers,  being  richest  in  starch  content. 

Symptoms.  White  rust  appears  late  when  the 
plants  have  usually  made  most  of  the  vine  growth  and 
when  the  hills  are  beginning  to  set,  i.  e. ,  to  form  new 
sweet  potatoes  in  the  soil.  A  typical  symptom  of 
white  rust  then  is  the  yellowing  of  leaves  in  the  center 
of  the  hill,  which  later  turn  brown,  shrivel,  and  die. 

In  carefully  examining  the  center  leaves  as  they 
begin  to  yellow,  we  see  that  on  the  under  side  of  such 
leaves  there  are  many  minute  white  raised  pimples, 
(fig.  25  e-f)  each  of  which  when  touched  with  the 


156  Diseases  of  Truck  Crops 

finger  sheds  a  white  dust  made  up  of  millions  of 
spores  of  the  fungus.  Each  white  pimple  on  the 
under  side  of  the  leaf  is  denoted  by  a  small  yellow 
area  on  the  upper  surface.  In  case  of  mild  infection 
there  are  usually  few  pimples  on  the  upper  leaf,  but 
when  the  disease  is  bad,  the  leaves  are  literally  pep- 
pered with  them.  White  rust  is  severest  when  the 
weather  is  dry  and  the  nights  are  cool.  It  is  also 
more  abundant  in  the  shaded  portions  of  the  field. 
With  the  exception  of  the  Southern  Queen,  all 
varieties  of  the  sweet  potato~grown  are  subject  to  it. 

SOFT  ROT 
Caused  by  Rhizopus  nigricans  Ehr. 

Soft  rot  is  mostly  a  storage  trouble,  although  it  is 
commonly  met  with  in  the  field  at  digging  time  and 
in  the  seed  bed.  It  is  constantly  associated  with 
poorly  ventilated  houses,  causing  more  damage  to 
stored  sweet  potatoes  than  all  other  diseases  com- 
bined. On  an  average,  fully  twenty  per  cent,  of  the 
total  crop  in  storage  is  lost  from  diseases  and  nine 
tenths  of  this  loss  may  be  attributed  to  soft  rot. 

Symptoms.  The  term  "soft  rot"  best  describes 
the  symptoms  of  the  disease.  Affected  roots  are 
very  soft  and  watersoaked,  and  when  pressed,  a  clear 
liquid  oozes  out.  Its  presence  in  the  bins  may  be 
detected  in  the  wetting  of  adjacent  healthy  roots. 
Under  storage  conditions,  infected  roots  do  not  pro- 
duce the  sporangia  of  Rhizopus  unless  broken  or 


Family  Convolvulaceae  157 

bruised.  Where  this  is  the  case,  a  black  mass  of 
short-stemmed  sporangia  or  fruiting  bodies  of  the 
fungus  are  formed  at  the  crack  (fig.  25  g),  through 
which  opening  the  liquid  from  the  root  drips.  When 
no  such  cracks  are  formed,  the  fungus  fails  to  fruit 
and  the  roots  dry  by  gradual  evaporation  through 
the  epidermis. 

Resistance  to  Soft  Rot.  While  soft  rot  causes  the 
greatest  damage  to  sweet  potatoes  in  storage,  not  all 
the  roots  alike  are  susceptible  to  its  attack.  There 
is  a  certain  per  cent,  of  the  crop  which  when  housed 
poorly  will  soft  rot  shortly  after  the  potatoes  are 
taken  into  storage,  while  another  per  cent,  seems  to 
possess  a  degree  of  resistance.  These  latter  will 
usually  keep  for  a  month  or  two  and  then  rot,  par- 
ticularly if  the  winter  is  mild  and  the  roots  undergo 
what  is  known  as  the  second  sweat.  There  is  a 
third  class  of  root  which  seems  to  be  resistant  for  a 
long  time. 

Odor  of  Soft  Rot.  Often  storage  men  claim  that 
soft  rot  emits  strong,  disagreeable  odors.  Observa- 
tions show  that  soft  rot  in  bins  is  odorless  for  a  week 
or  ten  days,  after  which  time  fermentation  sets  in, 
and  an  odor  is  quite  noticeable.  After  a  short  time, 
the  affected  potatoes  will  become  fairly  dried  out 
and  other  fungi  such  as  Diaporthe  batatis,  Fusarium 
batatatis,  Sderotium  bataticola,  and  a  number  of  sap- 
rophytic  fungi  gain  entrance.  Sometimes  putrefac- 
tion follows  the  acetic  fermentation. 

Soft  rot  is  not  carried  from  year  to  year  in  the 
dried-out  roots  which  were  previously  destroyed  by 


158  Diseases  of  Truck  Crops 

Rhizopus;  however,  the  spores  of  the  fungus  preserve 
their  vitality  for  a  considerable  time.  When  we 
consider  how  abundant  these  spores  are  in  nature, 
it  is  not  difficult  to  conceive  how  easy  it  is  for  soft 
rot  to  get  a  start  every  year.  The  storage  house  is 
undoubtedly  the  place  where  the  greatest  amount  of 
Rhizopus  spores  are  carried  over  from  year  to  year. 
The  main  problem,  therefore,  is  to  prevent  the  Rhizo- 
pus spores  from  germinating  or  to  use  some  fumigant 

which  will  kill  them  all  together. 

t 

RING  ROT 

Caused  by  Rhizopus  nigricans  Ehr. 

Ring  rot  is  a  form  of  soft  rot.  The  disease  is 
prevalent  as  soft  rot  and  is  found  in  poorly  venti- 
lated houses.  The  amount  of  loss  varies  from  I 
to  20  per  cent. 

Symptoms.  There  are  two  forms  of  ring  rot. 
The  first  stage  is  the  soft  ring  which  is  characterized 
by  a  rotted  area  which  girdles  the  root  at  any  point 
(fig.  25  h-i).  As  the  roots  are  usually  put  in  bins  in 
bulk  and  as  soft  ring,  like  soft  rot,  is  confined  to  the 
roots  more  or  less  buried  in  the  bulk  of  the  bin,  the 
onset  of  the  disease  is  usually  overlooked.  It  is  at 
first  odorless,  but  in  a  week  or  ten  days  it  is  followed 
by  a  characteristic  fermentation.  The  soft  ring 
gradually  begins  to  dry,  resulting  in  a  shrinkage  and 
contraction  of  this  area,  and  thus  a  slight  groove  is 
formed  (fig.  25  h).  In  two  to  six  weeks,  it  becomes 


FIG.  26.     SWEET  POTATO  DISEASES. 

a.  Black  rot  at  place  of  a  bruise,  b.  black  shank,  c.  showing  a  pycnidium  of  the 
black  rot  fungus,  d.  dry  rot,  e.  cross  section  through  /,  to  show  the  effect  of  the 
disease  on  the  root,  /.  Java  black  rot  surface  view,  showing  strings  of  spores  oozing 
out  from  the  center  of  spot,  g.  cross  section  through  .diseased  sweet  potato  root  to 
show  pycnidia  of  the  fungus  Diplodia  tubericola. 


Family  Convolvulaceae  159 

very  dry  and  more  or  less  hardened,  varying  with 
the  nature  of  the  fungi  which  act  as  secondary 
invaders.  The  second  form,  or  dry-ring  rot,  is 
nothing  more  than  the  last  or  dried-out  stage  of 
the  soft  ring  in  which  the  primary  parasite  has  died. 

DRY  ROT 
Caused  by  Diaporthe  batatis  (E.  and  H.)  H.  and  F. 

Dry  rot  is  a  disease  of  stored  sweet  potatoes. 
Although  it  has  a  wide  distribution,  the  trouble  is 
not  considered  of  great  economic  importance.  The 
disease  usually  follows  a  complication  of  others. 
It  begins  at  the  end  of  the  potato,  producing  a  firm 
dry  rot  which  progresses  slowly.  The  rotted  potato 
is  brown,  finally  becoming  hard  and  shriveled.  The 
surface  later  becomes  black,  rough,  and  uneven  (fig. 
26  d)  and  when  examined  under  the  microscope  will 
be  found  to  be  studded  with  numerous  pycnidia. 
From  the  mouths  of  the  latter  are  seen  to  ooze  out 
whitish  strings  which  are  made  up  of  millions  of  the 
pycnidia  or  summer  spores.  The  Diaporthe  or  as- 
cospores  are  formed  only  when  the  infected  roots  are 
allowed  to  hibernate. 

FOOT  ROT 

Caused  by  Plenodomus  destruens  Hart. 

Foot  rot  is  a  disease  which,  so  far  as  is  known,  is 
found  only  in  Virginia,  Ohio,  Iowa,  and  Missouri. 


160  Diseases  of  Truck  Crops 

Wherever  present  it  causes  serious  losses  to  sweet 
potatoes  in  the  field. 

Symptoms.  The  disease  first  manifests  itself  as 
sunken  brown  to  black  spots  at  the  stem  end  of  the 
plant  near  the  soil  line.  The  spots  gradually  enlarge, 
girdling  the  stem  and  working  upwards.  In  a  dis- 
eased field,  all  the  ends  of  the  vines  nearest  the  soil 
line  are  rotted,  so  that  the  entire  hill  may  be  easily 
pulled  out.  Although  the  feet  of  the  vines  in  a  dis- 
eased hill  rot  off,  the  vines  manage  to  remain  partly 
alive,  owing  to  the  nourishment  obtained  from  the 
secondary  rootlets  produced  at  the  leaf  nodes  on  the 
vines  which  lie  flat  on  the  ground.  Diseased  hills 
fail  to  produce  any  sweet  potatoes,  since  the  under- 
ground roots  are  cut  off  from  the  main  vines.  In- 
fection takes  place  in  the  field  or  in  the  seed  bed. 
Moisture  appears  to  favor  the  disease.  With  the 
death  of  the  vines  appears  a  pimply  growth  consist- 
ing of  numerous  pycnidia.  It  is  believed  that  foot  rot, 
like  many  other  sweet  potato  diseases,  is  carried  with 
the  seed.  The  fungus  Plenodomus  destruens  so  far  as  we 
know  possesses  only  the  pycnidial  or  summer  fruiting 
stage.  No  ascospore  stage  has  as  yet  been  found. 

BLACK  Rox1 
Caused  by  Sph&ronemafimbriatum  (E.  and  H.)  Sacc. 

Of  all  the  diseases  of  the  sweet  potato,  black  rot  is 
the  most  dreaded  by  growers.  It  is  found  in  all 

1  Material  drawn  from  the  author's  work.  Taubenhaus,  J.  J., 
Delaware  Agr.  Expt.  Sta.  Bui.  109  :  3-56,  1915. 


Family  Convolvulaceae  161 

sections  where  sweet  potatoes  are  grown.  Not  in- 
frequently the  disease  is  mistaken  for  other  troubles, 
and  too  often  its  nature  is  unknown  to  the  truckers. 

Symptoms.  Black  rot  is  a  seed-bed  disease,  a  field 
disease,  and  a  storage  trouble.  Irregular  dark  areas 
or  circular  spots,  varying  in  size  from  that  of  a  dime  to 
a  silver  dollar,  appear  on  the  seed  (seconds)  or  on  the 
prime  potatoes.  These  spots  extend  only  through 
the  skin  and  are  hard  to  the  touch.  When  the  roots 
are  injured  through  cultivation,  by  rodents,  or 
through  rough  handling  in  the  field  or  in  storage,  the 
spots  lose  their  circular  outline  and  follow  the  line 
of  injury  (fig.  26  a).  In  this  case  the  bruise  is  in- 
vaded by  secondary  parasites  which  may  induce 
rotting  of  the  entire  root. 

The  symptoms  shown  by  the  sprouts  are  a  dwarfing 
in  growth  and  yellowing  of  the  foliage.  In  this  latter 
case  the  end  of  the  shank  is  blackened  and  charred 
from  y£  to  I  inch  in  distance  (fig.  26  b).  Where  this 
stage  (known  as  the  " black  shank")  is  present,  the 
leaves  of  the  infected  sprouts  wither,  and  turn  black 
and  crisp.  Frequently  the  disease  affects  the  stem 
and  even  the  petioles  and  is  indicated  by  black  areas 
on  them.  In  early  stages  of  infection,  and  in  the 
absence  of  the  black  shank  stage,  the  rootlets  are 
usually  affected.  For  this  reason  it  is  essential  to 
examine  carefully  the  appearance  of  the  rootlets 
when  sprouts  are  pulled  from  the  field.  The  early 
symptoms  in  the  field  are  the  same  as  those  described 
for  the  sprouts  in  the  seed  bed.  Black  girdling  spots 
on  the  vines,  which  are  confined  to  areas  usually 

K 


1 62  Diseases  of  Truck  Crops 

between  two  leaves,  are  the  first  symptoms  on  the 
plant.  The  disease  seldom  blackens  the  full  length 
of  the  stem.  The  part  below  the  black  spot  remains 
healthy,  while  the  part  above  wilts  and  dies,  since 
the  infected  area  prevents  the  upward  flow  of  water 
and  plant  food  to  the  part  beyond  the  killed  area. 
Stem  infection  does  not  always  indicate  underground 
infection.  Often  where  the  vines  are  affected,  the 
roots,  when  pulled  out,  seem  to  be  free  from  black 
rot.  In  case  of  underground  infection,  sometimes 
every  root  in  the  hill  is  black  rotted  and  there  may 
not  be  the  least  indication  of  the  disease  on  the  stem 
of  the  plant.  At  digging  time,  roots  which  show  the 
disease  are  somewhat  paler  in  color  than  the  healthy 
ones  of  the  same  variety,  a  symptom  which  seems  to 
be  general  in  some  soils  and  not  in  others.  When 
roots  are  infected  with  black  rot,  the  edible  qualities 
are  poor  because  of  the  bitter  taste.  This  becomes 
more  marked  the  longer  the  roots  are  kept  in  storage. 
Although  the  black  rot  spot  is  only  superficial,  the 
bitter  taste  in  cooking  is  imparted  to  the  entire  root, 
showing  that  it  is  soluble  and  easily  diffused  into 
adjacent  tissue. 

Introduction  and  Spread  of  Black  Rot.  In  the  seed 
bed,  the  trouble  begins  with  diseased  seed.  Even 
though  the  greatest  care  is  exercised  in  discarding 
the  seed,  some  infected  roots  will  find  their  way  into 
the  bed.  Not  all  growers  are  careful  in  their  selec- 
tion of  seed,  and  often  through  lack  of  knowledge  of 
the  malady,  diseased  roots  are  used  in  bedding,  or  are 
discarded  and  thrown  out  near  the  bed.  These  seeds 


Family  Convolvulaceae  163 

are  then  trampled  upon  and  crushed  and  make  a  good 
starting  point  for  the  spread  of  black  rot.  As  the 
seed  begins  to  germinate,  the  sprouts  on  or  near  a 
mother  diseased  root  will  contract  the  disease.  On 
pulling  out  this  root,  nearly  every  sprout  will  show 
the  black  shank  which,  upon  careful  examination 
with  a  hand  lens,  will  be  found  to  be  strewn  with  the 
long-necked  pycnidia  of  the  fungus.  At  the  tip  of 
these  roots  are  seen  minute  waxy  droplets  which  con- 
sist of  the  pycnospores.  Small  mites,  white  minute 
spider-like  animals,  crawl  about  everywhere,  especi- 
ally on  and  around  the  pycnidia.  These  mites, 
as  well  as  watering,  help  to  spread  the  pycnospores 
in  the  seed  bed  and  result  in  the  further  infection  of 
new  sprouts. 

In  storage,  black  rot  is  first  introduced  with  dis- 
eased roots  and  is  spread  from  one  to  another,  fruit- 
ing best  in  the  presence  of  moisture.  In  poorly 
ventilated  houses,  it  is  invariably  noticed  as  soon 
as  the  roots  begin  to  sprout.  These  sprouts  turn 
black  and  die  at  the  tender  tip  or  throughout.  In 
the  first  stage,  while  growing  in  the  interior  tissue, 
the  fungus  does  not  produce  pycnidia.  Therefore,  as 
long  as  the  epidermis  on  the  spot  is  unbroken  and  the 
roots  are  kept  dry,  the  disease  cannot  spread.  How- 
ever, if  the  skin  is  broken  or  accidentally  bruised,  or  if 
the  roots  are  kept  in  a  house  which  is  overheated  and 
damp,  the  black  rot  fungus  will  produce  fruit  by  the 
formation  of  pycnidia  which  appear  as  minute  raised 
dots  in  the  center  of  the  spot. 

The  Organism.    The  parasite  consists  of  a  vegeta- 


1 64  Diseases  of  Truck  Crops 

tive  portion  known  as  "mycelium*1  which,  when 
young,  is  hyaline,  but  which  becomes  gray  with  age. 
Whether  young  or  old,  they  are  capable  of  breaking 
up  into  as  many  cells  as  there  are  septa,  and  each  cell 
may  assume  the  function  of  a  spore,  since  it  will 
readily  germinate.  In  another  stage,  chains  of 
hyaline  spores  are  born  and  pushed  out  from  within 
long  terminal  cells  of  the  mycelium.  The  chlamy do- 
spores  apparently  serve  as  resting  spores  to  carry  the 
fungus  over  winter,  and  the  cells  of  the  infected  tissue 
are  usually  filled  with  these  brown  thick-walled  spores. 
A  last  stage  is  that  of  pycnospores  which  are  born 
within  long-necked  spore  sacks  called  pycnidia  (fig. 
26  c).  These  are  minute  globular  spores  oozing  out 
in  a  gelatinous  mass  which  stick  to  the  open  end  of 
the  long  neck  of  the  pycnidium.  In  pure  cultures 
the  spores  ooze  out  in  strings  just  as  in  the  case 
of  certain  species  of  Phoma  or  Phyllosticta.  The 
spores  can  germinate  in  water  or  in  any  nutritive 
fluid. 

PHYLLOSTICTA  LEAF  BLIGHT 
Caused  by  Phyllosticta  batatas  E.  and  M.t 

Leaf  blight  appears  as  roundish  to  angular  spots 
on  the  upper  side  of  the  leaf  and  is  separated  from 
the  healthy  tissue  by  a  dark  line.  Inside  this  line  is 
a  strip  of  brownish  tissue  which  has  lost  most  of  the 
green  color.  Within  this  ring  is  a  circular  area  much 
lighter  in  color  in  which  the  pycnidia  are  found 


Family  Convolvulaceae  165 

protruding.     The  fungus,  so  far  as  is  known,  lives 
only  on  sweet  potato  foliage. 

SEPTORIA  LEAF  SPOT 
Caused  by  Septoria  bataticola  Taub. 

Leaf  spot  is  a  disease  which  is  of  little  economic 
importance.  The  trouble  appears  as  soon  as  the 
plants  attain  full  growth  and  are  beginning  to 
lose  in  vigor.  The  disease  has  been  found  in  New 
Jersey,  Delaware,  Maryland,  Virginia,  Iowa,  and 
other  States. 

Symptoms.  Leaf  spot  is  characterized  by  small 
whitish  spots  scattered  indiscriminately  over  the 
leaf.  The  spots  are  nearly  always  surrounded  by 
a  brown  border  (fig.  27  b).  On  the  surface  of  the 
dead  tissue  are  found  the  pycnidia  which  are  usually 
few  in  numbers,  often  not  more  than  one  or  two  to  a 
spot.  The  pycnospores  are  carried  about  from  leaf 
to  leaf  by  winds  or  insects. 

Septoria  bataticola  attacks  only  sweet  potato  foliage. 
It  is  very  likely  that  the  fungus  hibernates  on  the 
dead  leaves  in  the  field.  Leaf  spot  is  never  serious 
enough  to  warrant  special  methods  of  control. 

JAVA  BLACK  ROT 
Caused  by  Diplodia  tubericola  (E.  and  E.)  Taub. 

The  disease  was  first  found  on  some  sweet  potatoes 
that  were  brought  to  the  Louisiana  station  from 
Java  in  the  spring  of  1894.  The  potatoes  appeared 


166  Diseases  of  Truck  Crops 

sound,  but  failed  to  grow  when  planted.  Upon 
examination  the  roots  were  found  to  be  rotted.  The 
fungus  which  caused  the  rot  was  sent  to  Ellis,  who 
identified  it  as  a  new  genus  and  gave  it  the  name  of 
Lasiodiplodia  tubericola.  Sweet  potatoes  brought 
from  Java  in  the  spring  of  1895  were  found  to  be 
affected  with  the  same  fungus  when  they  were  re- 
ceived at  Baton  Rouge.  This  seems  to  indicate  that 
the  fungus  was  introduced  in  the  United  States  from 
Java. 

Symptoms.  Sweet  potatoes  affected  by  the  fungus 
show  dark  shriveled  patches  over  which  are  scattered 
numerous  pycnidia.  These  emit  either  mature  one- 
septate  dark  spores  of  Diplodia  type,  heaped  to- 
gether, or  white  strings  (fig.  26  f),  which  are  made  up 
of  hyaline  Macrophoma  spores,  or  both  (fig.  26  f) . 
In  making  longitudinal  sections  through  different 
stages  of  affected  roots,  it  will  be  found  that  the  fun- 
gus attacks  the  interior  tissue,  beginning  at  the  point 
and  gradually  invading  the  whole  of  the  interior  of 
the  root.  The  infected  tissue  is  jet-black  (fig.  26  e), 
somewhat  resembling  the  charcoal  disease.  In- 
fected roots  dry  and  shrivel  and  become  brittle. 
Complete  rotting  of  the  root  is  effected  in  four  to 
eight  weeks.  The  active  enzyme  from  the  fungus 
precedes  the  mycelium  some  distance,  for  in  a  longi- 
tudinal section  of  a  newly  infected  root  two  zones 
may  be  observed,  one,  a  dark  area  which  is  occupied 
by  the  fungus,  and  the  other,  a  brown  zone  which 
precedes  the  dark  patch  in  which  the  mycelium  is 
absent.  The  pycnidia  are  born  singly  or  in  groups 


FIG.  27.     SWEET  POTATO  DISEASES. 

a.  Trichoderma  rot,  b.  Septoria  leaf  spot,  c.  soil  stain,  J.  Charcoal  rot,  e.  Texas 
root  rot:  notice  the  center  of  the  hill  is  dead,  while  the  side  shoots  are  alive  as  they 
are  supported  by  the  secondary  roots  formed  at  the  nodes  of  the  vines,  /.  sweet 
potato  artificially  inoculated  with  Sclerolium  Rolfsii,  g.  net  necrosis. 


Family  Convolvulaceae  167 

under  the  epidermis,  and  the  latter  is  ruptured  at  an 
early  stage  (fig.  26  f).  They  are  also  formed  through 
the  interior  tissue  of  the  infected  root,  and  it  seems 
that  in  this  case  the  spores  can  escape  only  when  the 
roots  break  up  and  disintegrate. x 

TRICHODERMA  ROT 

Caused  by  Trichoderma  Koningi  Oud.,  and  Tricho- 
derma  lignorum  (Tode.)  Harz. 

The  symptoms  of  several  of  the  different  rots  on  the 
sweet  potato  are  often  so  similar  that  it  is  difficult  to 
find  appropriate,  popular  names  with  which  to  char- 
acterize each  disease.  Trichoderma  rot  by  itself 
does  not  exist  under  the  average  storage  conditions. 
But  it  follows  other  rots,  particularly  ring  rot,  and 
soft  rot,  causing  further  destruction  of  the  partially 
affected  roots.  Trichoderma  rot  is  a  storage  trouble 
only,  and  the  causative  organism  is  no  doubt  brought 
in  from  the  field  adhering  to  particles  of  soil. 

Symptom.  In  the  earliest  stages,  the  spots  are 
circular,  and  of  a  light  brown  color,  with  a  tendency 
to  wrinkle.  The  flesh  is  hard  and  watersoaked, 
brown  in  color  with  a  black  zone  in  the  region  be- 
tween the  healthy  and  diseased  tissue  (fig.  27  a). 
The  spot  enlarges  in  all  directions  and  eventually 
destroys  the  entire  root.  When  the  decay  is  well 
advanced,  a  very  luxuriant,  white,  mycelial  growth 
is  formed  on  the  surface.  Spores  are  produced  very 

1  For  further  details  of  this  fungus  see  Taubenhaus,  J.  J.,  Ameri- 
can Jour,  of  Bot.,  2  : 324-3-31,  1915. 


1 68  Diseases  of  Truck  Crops 

sparingly  from  this  growth  when  in  contact  with  the 
decayed  tissue,  but  very  abundantly  on  that  part  of 
the  mycelium  which  has  spread  over  the  healthy  sur- 
face or  into  the  glass  or  filter  paper  of  the  moist  cham- 
ber. Trichoderma  lignorum  is  common  and  widely 
distributed  on  decaying  wood  and  various  other  sub- 
stances. Trichoderma  Koningi  was  originally  iso- 
lated from  the  soil  by  Oudemans  and  is  still  looked 
upon  as  a  soil  organism.  The  spores  are  elliptical  and 
are  borne  on  characteristic  conidiophores  (fig.  28  p). 

SOIL  STAIN  OR  SCURF 
Caused  by  Monilochaetes  infuscans  E.  and  E. 

Soil  stain  is  not  a  disease  to  be  feared  in  the  sense 
that  it  may  produce  a  direct  rot  in  the  mature  roots. 
Nevertheless,  it  is  economically  important.  Growers 
whose  lands  are  badly  infected  assert  that  stained 
roots  keep  better  in  storage.  Others  find  consolation 
in  saying,  "There  is  no  such  thing  as  stain,  the  dark 
color  of  the  skin  being  merely  a  varietal  character- 
istic." The  fact  remains,  however,  that  many 
Eastern  markets  discriminate  against  stained  roots. 
In  years  of  over-production  the  New  York  market 
refuses  stained  roots  altogether.  The  Western  buy- 
ers, on  the  contrary,  are  lax  on  this  point;  other- 
wise, many  growers  in  the  United  States  would  be 
forced  to  cease  producing  sweet  potatoes  for  want 
of  a  market,  since  soil  stain  is  prevalent  on  practi- 
cally all  sweet-potato  land. 

Symptoms.  Soil  stain  is  characterized  at  first  by 
small,  circular,  deep  clay-colored  spots  on  the  surface 


Family  Convolvulaceae  169 

of  the  sweet  potato  root.  These  spots  occur  singly; 
but  usually  several  occur  in  a  given  area.  When 
very  numerous,  the  spots  coalesce,  forming  a  large 
blotch,  which  sometimes  takes  the  form  of  a  band, 
or  which  may  cover  the  entire  root.  Soil  stain  is 
particularly  conspicuous  on  the  white-skinned  varie- 
ties, such  as  the  Southern  Queen.  Here  the  color  of 
the  spots  is  that  of  a  deep-black  clay  loam.  On  the 
darker-skinned  varieties  the  color  of  the  spots  does 
not  appear  so  conspicuous.  Soil  stain  is  a  disease  of 
the  underground  parts  of  the  plant.  The  vines  and 
foliage  are  never  attacked  so  long  as  they  remain  free 
from  the  soil.  But  when  they  are  covered,  the  peti- 
oles as  well  as  the  stems  become  infected. 

After  several  months  of  storage,  badly  affected 
roots  become  a  deep  brown,  contrasting  strongly  with 
non-infected  potatoes.  Occasionally,  badly  stained 
roots  seem  to  be  subject  to  more  rapid  drying  and 
shrinking.  This,  however,  is  not  often  the  rule. 
Usually  soil  stain  is  prevalent  in  over-heated  storage 
houses.  It  may  be,  therefore,  that  the  rapid  shrink- 
age is  due  to  the  overheating  and  not  to  the  effect  of 
the  disease  itself.  More  data  are  necessary  to  deter- 
mine this  point.  Soil  stain  is  a  disease  not  only  of  the 
epidermis  that  considerably  reduces  the  market  value 
of  the  mature  roots,  but  it  also  attacks  the  very 
young  rootlets,  preventing  their  further  development 
and  indirectly  reducing  the  yield.  In  badly  affected 
fields  the  writer  has  estimated  a  loss  of  10  per  cent,  of 
the  crop  from  the  rootlet  infection. 

The  type  of  soil  seems  to  be  a  determining  factor 


170  Diseases  of  Truck  Crops 

in  the  development  of  soil  stain.  Sweet  potatoes, 
grown  on  very  light  sandy  soils,  especially  those 
which  are  hilly,  are  usually  free  from  the  disease. 
Heavier  lands,  or  those  rich  in  humus,  rarely  produce 
a  clean  crop.  The  application  of  manure  favors  the 
spread  of  the  fungus  and  increases  the  stain.  In 
fact,  the  manure  itself  is  often  a  carrier  of  the  disease, 
since  diseased  roots  of  all  sorts  find  their  way 
ultimately  to  the  manure  pile.  The  trouble  is  also 
carried  directly  with  the  seed  stock.  This,  when 
planted  in  the  seed  bed  in  diseased  condition,  will 
produce  100  per  cent,  of  diseased  sprouts.  Wet 
weather  is  favorable  to  the  spread  and  increase  of 
stain.  During  wet  seasons  the  disease  is  more 
plentiful  than  in  dry  seasons. 

The  Organism.  The  spores  are  born  in  distinct 
chains  which  break  up  very  readily  when  moistened 
(fig.  28  a-1).  The  conidiophores  are  born  on  the 
surface  of  the  epidermis  (fig.  28  n).  Careful  ob- 
servation of  these  chains  have  shown  them  to  be 
made  up  of  from  10  to  28  conidia.  The  spores  (con- 
idia)  are  one  celled,  hyaline,  with  a  greenish  tinge, 
but  never  dark  or  brown.  The  spores  readily  germi- 
nate in  water  or  in  any  nutrient  medium  (fig.  28  o). 

VINE  WILT  OR  YELLOWS  (STEM  ROT) 

Caused  by  Fusarium  batatatis  Woll.     Fusarium 
hyperoxysporum  Woll. 

The  terms  "stem  wilt,"  "vine  wilt,"  or  "yellows" 
are  commonly  used  to  describe  this  disease,  and 


a 


FIG.  28.     SWEET  POTATO  DISEASES. 

a.  and  i.  Chains  of  conidia  of  the  soil  stain  fungus  Monilochceles  infuscans, 
b.  to  I.  manner  in  which  the  chains  of  conidia  of  M.  infuscans  are  breaking  up 
into  individual  spores,  o.  germinating  conidia  of  M.  infuscans,  n.  part  of  a 
cross  section  of  a  sweet  potato  root  showing  the  relationship  of  M .  infuscans 
to  the  epidermis  of  the  host,  p.  conidiophores  of  Trichoderma  Koningi,  a, 
young  strands  of  mycelium  of  Phymatotrichum  omnivorum,  r.  mycelial  strands 
of  the  Texas  root  rot  fungus,  Ozonium  omnivorum  from  dead  cotton  plant  (q. 
and  r.  after  Duggar),  m.  sclerotia  of  Sderotium  bataticola. 


Family  Convolvulaceae  171 

they  are  more  appropriate  than  the  name  "stem 
rot." 

Symptoms.  There  is  no  doubt  that  "stem  wilt" 
has  its  origin  in  the  seed  bed.  In  badly  infected 
soils,  it  is  often  difficult  for  the  plants  to  get  a  stand, 
as  they  die  a  week  or  two  after  being  put  out.  They 
first  lose  their  green  color,  and  turn  pale,  and' when 
they  are  pulled  out,  they  will  be  found  to  be  cracked 
lengthwise  because  of  the  swelling.  The  presence  of 
stem  wilt  may  easily  be  determined  by  inserting  the 
nail  into  the  stem  and  peeling  off  a  piece  of  epidermis 
and  cambium ;  the  vessels  will  be  found  to  be  a  brown 
color.  Frequently  the  stem  is  covered  with  a  pink- 
ish layer  of  sickle-shaped  spores  of  the  Fusarium 
parasite.  Often,  and  particularly  in  moist  seasons, 
infected  sprouts  continue  to  grow,  sometimes  until 
digging  time,  and  even  produce  fair  sized  roots,  pro- 
vided no  secondary  invaders  set  in  to  destroy  the 
hill.  Sometimes  black  rot,  as  a  secondary  parasite, 
sets  in  at  the  base  of  the  stem  near  the  ground,  kill- 
ing the  bark  or  covering  of  the  stem,  thus  shutting 
off  all  food  supply,  and  resulting  in  the  dying  of  the 
entire  hill  in  a  short  time.  Frequently  a  wet  bacte- 
rial rot  starts  in  the  base  of  the  plant  where  black  rot 
has  followed  stem  wilt.  This  stage  helps  to  convey 
the  erroneous  impression  that  stem  wilt  induces  an 
actual  rotting  in  the  field.  Yellowing  of  the  affected 
stems  and  vines,  while  a  frequent  symptom,  is  not 
always  pronounced.  Often  the  disease  in  plants 
can  hardly  be  detected,  as  the  fungus  is  hidden  inter- 
nally in  the  fibro-vascular  bundles  and  the  roots  main- 


172  Diseases  of  Truck  Crops 

tain  a  thriving  green  appearance.  In  clipping  the 
tip  end  of  such  a  root,  the  bundles  appear  brown  in 
color,  and  usually  the  disease  may  be  traced*through 
the  entire  length  of  the  root.  Sometimes  only  a  few 
bundles  in  •  the  root  are  affected,  while  in  others 
each  shows  the  brown  ring  near  the  cambium.  It 
is  better  that  the  affected  sprouts  should  die 
early,  for  if  they  grow  and  produce  roots  of  the 
No.  2  type,  they  carry  the  disease  to  the  seed  bed. 
This  is  more  of  a  field  than  a  storage  trouble.  In 
large  and  badly  infected  roots  in  storage,  the 
fungus  may  produce  a  punky,  dry  rot  which  has 
a  peculiar  cinnamon  odor  and  a  deep  chocolate 
color  which  may  make  the  roots  light  and  shriveled 
(see  fig.  27  a-e). 

A  diseased  hill  one  year  will  mean  several  diseased 
hills  the  following  year.  In  plowing  up  the  land  for 
sweet  potatoes  the  original  hill  is  broken,  and  the 
stem  wilt  fungus  is  carried  some  distance  in  both 
directions  by  the  plow  and  the  harrow.  The  culti- 
vator, too,  may,  during  the  season,  help  to  carry  the 
disease  and  induce  new  infections  by  injuring  the 
sprouts.  Dead  sprouts  and  dead  hills,  if  left  over 
in  the  field,  furnish  material  on  which  the  fungus  will 
fruit  abundantly. 

The  two  organisms  greatly  resemble  each  other  in 
spore  form  (fig.  7  c-d).  Yellows  is  prevalent  in  New 
Jersey,  Maryland,  Virginia,  Illinois,  Iowa,  Alabama, 
Arkansas,  Missouri,  North  Carolina,  Ohio,  Georgia, 
Texas,  Oklahoma,  and  Mississippi.  A  conservative 
estimate  of  the  losses  from  yellows  would  be  at  least 


Family  Convolvulace^e  173 

three  quarters  of  a  million  for  the  entire  sweet  potato 
crop  of  the  United  States.   > 

CHARCOAL  ROT 
Caused  by  Sclerotium  bataticola  Taub. 

"Charcoal  rot"  is  a  new  name  for  an  old  trouble. 
It  is  mainly  a  storage  trouble  and  is  found  most  com- 
monly in  overcrowded  houses  and  in  bins  nearest  the 
stoves.  It  is  especially  plentiful  in  houses  which 
lose  heavily  from  soft  rot.  After  the  work  of  Hal- 
sted,  from  1890  to  1913,  the  fungus  which  caused 
charcoal  rot  was  believed  to  be  a  stage  of  the  black 
rot  fungus.  But  it  has  been  shown  by  the  writer  that 
charcoal  rot  is  a  distinct  disease  and  that  the  fungus 
which  causes  it  is  in  no  way  connected  with  or  re- 
lated to  the  black  rot  organism,  Sph&ronema  fim- 
briatum  (E.  and  H.)  Sacc. 

Charcoal  rot  is  commonly  mistaken  for  black  rot. 
While  black  rot  produces  only  superficial  spots  on  the 
roots,  and  does  not  produce  a  rot  of  the  entire  root, 
charcoal  rot  is  a  disease  which  penetrates  the  entire 
root.  The  parasite  does  not  produce  surface  spots, 
but  turns  the  interior  tissue  into  a  black  charcoal 
mass  (fig.  27  d)  caused  by  the  formation  of  minute 
colored  sclerotia  (fig.  28  m).  With  the  exception  of 
drying  and  slight  shrinkage,  there  are  no  external 
symptoms  to  distinguish  the  disease  unless  the  skin 
is  bruised,  showing  the  blackened  contents.  It  can 
be  recognized  when  the  roots  have  been  completely 
invaded.  Recent  studies  on  this  disease  seem  to 


174  Diseases  of  Truck  Crops 

indicate  that  infection  takes  place  from  a  bruise  on 
the  epidermis  and  from  there  the  fungus  works  slowly 
inward.  It  is  not  uncommon,  therefore,  in  slight 
cases  of  infection,  to  find,  upon  making  a  cross  section 
of  the  root,  a  jet  black  ring  ranging  from  one  third 
to  one  half  an  inch  in  diameter  immediately  under  the 
epidermis,  the  color  grading  off  from  dark  to  a  light  ash 
as  it  nears  the  center  of  the  root.  At  this  stage  the 
infected  sweet  potato  is  watersoaked  but  quite  solid. 
A  liquid,  brownish  in  color,  may  be  squeezed  from 
such  roots.  Charcoal  rot  is  almost  unknown  in  well 
ventilated  houses.  There  seems  little  doubt  that 
the  fungus  5.  bataticola  is  a  common  field  saprophyte, 
which  may  be  brought  into  the  storage  house  with 
the  sand  or  soil  which  clings  to  the  roots.  Diseased 
roots  kept  dry  for  one  year  will  readily  yield  a  pure 
culture  of  the  fungus,  thus  showing  that  these  roots 
carry  the  fungus  from  year  to  year. 

The  Organism.  The  sclerotia  are  jet  black,  very 
minute,  smooth,  and  made  up  exteriorly  of  anasto- 
mosed black  hyphas.  The  interior  of  the  sclerotia  is 
light  to  dark  brown,  composed  of  thick  walled  cortical 
hyphal  cells  (fig.  28  m).  The  sclerotia  appear  singly, 
and  oftentimes  in  long  chains,  and  abound  through- 
out the  entire  affected  root. 

COTTONY  ROT 

Caused  by  Sclerotium  Roljsii  Sacc. 

Cottony  rot  is  mostly  a  disease  of  the  seed  bed. 
Infected  sprouts  suddenly  wilt  and  topple  over,  giv- 


Family  Convolvulaceae  175 

ing  the  effect  of  damping  off.  In  examining  an 
infected  sprout  it  will  be  found  that  in  the  earlier 
stages  of  attack  the  foot  of  the  plant  is  soft,  water- 
soaked,  and  covered  at  the  exterior  by  fungus 
threads.  Later  this  growth  becomes  thick,  giving 
the  appearance  of  fluffy  cotton  placed  at  the  foot  of 
the  sprout.  Soon  after,  the  cottony  mycelial  growth 
anastomoses,  then  disappears,  giving  birth  to  small 
roundish  brown  bodies  like  mustard  seed  known  as 
sclerotia. 

Sclerotium  Rolfsii  seldom  attacks  mature  sweet 
potato  roots.  However,  when  the  fungus  is  arti- 
ficially inoculated  in  sound  roots,  a  punky  dry  but 
slow  rot  is  the  result  (fig.  27  f).  For  further  dis- 
cussion of  this  fungus  as  it  attacks  other  hosts  see 
P-  305. 

TEXAS  ROOT  ROT 
Caused  by  Ozonium  omnivorum  Shear. 

So  far  as  is  known,  this  disease  occurs  only  in  Texas, 
New  Mexico,  Oklahoma,  and  Arizona.  The  disease 
is  of  great  economic  importance  in  these  States,  since 
numerous  other  crops  are  subject  to  its  attacks. 
The  symptoms  of  Texas  root  rot  are  a  girdling  of  the 
vines  at  the  stem  end,  and  a  similar  effect  on  the  roots 
(fig.  27  e  and  fig.  28  g  and  r).  In  these  cases,  the 
epidermis  and  cambium  may  be  readily  slipped  off 
from  the  main  body  of  the  infected  stem  and  root. 
For  a  more  detailed  account  of  the  Texas  root  rot, 
see  okra,  p.  297. 


176  Diseases  of  Truck  Crops 

ROOT^KNOT 
•     Caused  by  Heterodera  radicicola  (Greef)  Mull. 

Root  knot  of  sweet  potatoes  is  commonly  found  in 
the  Southern  States  in  light  sandy  soils.  It  is  char- 
acterized by  small  swellings  on  the  lateral  feeding 
roots.  For  further  description,  see  p.  49. 

METHODS  OF  CONTROLLING  SWEET  POTATO  DISEASES 

The  grower  in  dealing  with  sweet  potato  diseases 
has  a  fourfold  problem.  No  amount  of  care  will 
suffice  to  keep  down  his  losses  from  disease,  unless 
he  handles  the  problem  thoroughly,  beginning  with 
the  seed  and  continuing  through  the  seed  bed,  the 
field,  and  the  storage  house.  No  one  method  of 
control  will  suffice  alone;  each  phase  must  be  dealt 
with  separately. 

Methods  of  Obtaining  Seed  Free  from  Disease.  The 
selection  of  clean  seed  from  bins,  while  working  suc- 
cessfully with  other  crops,  is  not  to  be  practiced  in 
the  case  of  sweet  potatoes,  since  much  disease  is 
carried  inside  of  the  roots  or  in  the  dust  which  coats 
them.  Seed  treatment  should  be  preceded  by  seed 
selection.  The  use  of  seconds  for  seed  is  not  satis- 
factory, since  they  may  be  the  small  roots  produced 
from  diseased  hills,  and  hence  carriers  of  disease. 

The  use  of  slips  is  very  desirable,  since  in  this  case 
a  beginning  is  made  with  healthy  cuttings  from  which 
hills  of  slip  seed  are  produced.  These  in  turn  are 
healthy,  since  they  are  not  hampered  by  disease 


Family  Convolvulaceae  177 

from  the  mother  cuttings.  However  the  growing  of 
slip  seed  every  year  is  a  tedious  process.  To  im- 
prove the  strain  and  avoid  disease  slip  seed  may  be 
grown  every  second  or  third  year,  from  hill  selected 
primes.  Following  the  use  of  such  slip  seed,  primes 
may  be  used  for  one  or  two  seasons,  to  be  followed 
again  by  a  high  strain  of  slip  seed.  Roots  which  are 
round,  chunky,  and  smooth  should  be  chosen.  Seeds 
which  have  sprouted  in  storage  should  be  discarded, 
as  these  roots  often  carry  diseases.  The  seed  of  some 
varieties,  however,  are  known  always  to  sprout,  no 
matter  under  what  storage  conditions  they  are  kept. 
In  these  cases,  the  sprouts  should  be  broken  or  rubbed 
off  and  the  seed  be  treated  with  corrosive  sublimate 
before  being  bedded.  No  injury  results  from  this 
process  and  new  sprouts  soon  follow.  As  the  seeds 
are  being  carefully  selected  one  by  one,  the  stem  end 
of  each  root  should  be  clipped  off  with  a  sharp  knife  to 
a  distance  of  one  third  of  an  inch.  Every  cut  surface 
should  present  a  clean  white  appearance.  Brown 
spots  in  the  interior  of  the  root  mean  the  presence  of 
disease  in  the  vessels.  Such  seeds  should  be  discarded, 
even  though  the  exterior  is  healthy  looking.  In  us- 
ing primes  for  seeds,  selection  should  be  made  in  the 
fall  at  digging  time.  The  roots  from  the  highest  yield- 
ing and  healthiest  hills  should  be  chosen,  marked,  and 
stored  separately  under  the  best  possible  conditions. 
Before  bedding,  these  should  be  sorted  over  again  and 
the  stem  ends  of  the  most  choice  should  be  clipped  to 
make  sure  of  their  freedom  from  internal  disease. 
Seed  Treatment.  Having  selected  good  sound  seeds, 

12 


1 78  Diseases  of  Truck  Crops 

it  is  not  wise  to  bed  them  untreated.  In  using  prime 
seed  they  might  easily  soft  rot  in  the  bed.  This 
rotting  may  be  increased  where  the  ends  are  clipped. 
To  obviate  this  possibility  and  to  destroy  the  spores 
of  disease,  the  seed  should  be  disinfected  with  a  solu- 
tion of  corrosive  sublimate  made  up  of  one  ounce  of 
the  chemical  dissolved  in  eight  gallons  of  water,  and 
the  seed  soaked  for  ten  minutes.  Usually  it  is 
advisable  to  treat  one  bushel  at  a  time.  For  large 
quantities  of  seed,  100  to  200  gallons  of  the  solution 
may  be  prepared  in  several  fifty  gallon  barrels. 

Besides  treating  the  seed,  the  soil  in  the  seed  bed 
must  be  disinfected.  This  may  be  done  with  the 
steam  method,  see  pages  54-56,  or  with  the  for- 
maldehyde method,  page  53. 

Where  flue,  hot  water,  or  manure  heated  beds  are 
used  permanently,  the  wooden  framework  should  be 
disinfected  every  year  by  thoroughly  sprinkling  or 
soaking  with  corrosive  sublimate  solution  or  the 
formaldehyde  solution  of  the  same  strength  as  used 
for  the  seed.  As  soon  as  the  framework  begins  to 
rot,  it  should  be  discarded. 

FIELD  METHODS  OF  CONTROL 

The  grower's  efforts  to  stamp  out  the  diseases  of 
the  sweet  potato  cannot  stop  with  care  that  the  seed 
shall  be  healthy  and  the  seed  bed  clean.  It  has  al- 
ready been  shown  that  several  diseases  like  black 
rot,  stem  wilt,  ground  rot  or  pit,  and  soilstain  may  be 
and  are  carried  over  in  the  soil.  These  diseases  con- 


Family  Convolvulaceae  179 

stantly  spread  and  increase  in  the  land,  as  the  sweet 
potato  is  grown  continuously  on  the  same  ground. 
This  being  the  case,  we  cannot  expect  healthy  plants 
to  thrive  or  be  free  from  disease  on  land  that  is  badly 
infected  with  disease.  Cleanliness  is,  therefore,  the 
only  means  of  keeping  out  disease  from  fields  de- 
voted to  sweet  potatoes. 

Sprout  Treatment.  Before  being  planted,  sprouts 
should  be  treated,  in  order  to  insure  the  best  stand. 
Not  only  are  untreated  sprouts  subject  to  chance  con- 
tamination, but  they  are  also  the  prey  to  flea  beetles 
as  soon  as  they  are  planted.  When  the  sprouts  are 
pulled  from  the  seed  bed  they  should  be  taken  at 
once  to  a  shaded  place  and  dipped  into  a  Bordeaux 
mixture,  3-3-5°- 

Other  Field  Control  Measures.  Growers  will  do 
well  to  make  it  a  point  to  inspect  their  fields  every 
week  or  two  and  pull  out  and  burn  stunted  plants 
which  are  yellow,  sickly  looking,  and  which  fail  to 
grow.  These  should  never  be  left  near  the  seed  bed, 
but  should  be  destroyed  so  that  the  disease  cannot 
spread  to  the  healthy  plants.  Clean  cultivation  is 
essential  in  preventing  field  diseases  with  the  sweet 
potato.  In  cultivation,  great  care  should  be  taken 
to  prevent  injury  to  the  roots,  as  an  injury  means 
a  possible  opening  for  disease. 

STORAGE  METHODS  OF  CONTROL 

Before  satisfactory  conditions  can  be  found  for  the 
proper  storing  of  sweet  potatoes,  there  must  be  a 


i8o  Diseases  of  Truck  Crops 

clear  understanding  of  the  storage  problem.  Investi- 
gations have  shown  definitely  that  the  greatest  loss 
from  disease  in  storage  is  due  to  soft  rot.  It  has  been 
estimated  that  90%  of  the  loss  is  due  to  this  one 
disease,  9%  to  black  rot,  and  i%  to  all  other  rots. 

Table  14  gives  part  of  the  data  collected  in  Novem- 
ber, 1909,  at  the  storage  house  of  Huston  Darbee, 
Seaford,  Del.  The  thermometer  readings  are  re- 
corded in  Fahrenheit  degrees  and  the  compara- 
tive moisture  readings  are  taken  with  Mitthof's 
hygrometers.  Whenever  the  readings  of  the  hy- 
grometer run  over  70  and  remain  there  for  some 
time,  soft  rot  sooner  or  later  sets  in. 

Table  14  also  shows  that  not  only  is  the  tempera- 
ture different  in  the  different  parts  of  the  same  floor, 
but  that  it  differs  on  different  floors.  Any  ventila- 
tion which  will  bring  down  the  moisture  content  ten  or 
twelve  per  cent,  will  help  keep  sweet  potatoes.  How- 
ever, natural  ventilation  will  not  always  accomplish 
this,  since  the  moisture  content  of  the  outside  air  is 
the  great  governing  factor.  For  instance,  it  is  seen 
in  Table  14  that  from  the  ist  to  the  5th  of  November, 
1913,  the  weather  was  fair  and  the  air  dry;  hence  by 
opening  up  doors  and  windows  in  the  morning,  the 
moisture  readings  were  greatly  reduced.  However, 
on  the  7th,  the  moisture  increased  when  the  ventila- 
tors were  opened  on  the  first  floor.  A  fair  day,  there- 
fore, does  not  always  indicate  dry  air,  just  as  a  cloudy 
day  does  not  always  mean  moist  air,  as  is  indicated 
by  the  hygrometer  readings  on  both  floors  during  the 
1 4th  of  November.  Rainy  days  and  damp  weather 


Family  Convolvulacese 


181 


offer  no  opportunity  for  the  lowering  of  the  moisture, 
as  will  be  seen  on  November  i6th,  when  opening  the 

LTABLE    14 

Storage  Temperature  and  Moisture  Reading  for  November,  1909,  for 

1st  and  jd  Floors. 


Thermometer  Reading 

First  Floor 

Ther. 

Moist. 

Moist. 

Read. 

Read. 

Read. 

Outdoor 

Date 

East  Side 

West 

Third 
Floor 

First 
Floor 

Third 
Floor 

Temp. 

Kind  of  Day 

of  House 

Side 

A.M.    P.M. 

A.M.    P.M. 

A.M.    P.M. 

A.M.    P.M. 

A.M.    P.M. 

A.M.    P.M. 

I 

54      50 

50       54 

57       57 

62      49 

66      46 

32      48 

Fair 

2 

46       53 

50      58 

57       62 

65      55 

6?      57 

38      54 

Pair 

3 

42       S3 

45      60 

55       60 

67      46 

70      42 

33       52 

Fair 

4 

52       56 

56      63 

57       62 

68      54 

65      50 

54      60 

Fair 

5 
6 

46      52 

41       S3 

48       57 
44      60 

56      60 

52       62 

63      52 
67      60 

65      48 
68      47 

37       54 
30      60 

Fair 
Fair 

7 

43       54 

49      60 

54      64 

68      72 

67      60 

35      64 

Fair 

8 

S3       58 

58      64 

59      66 

80       77 

70      67 

54      60 

Fair  and  cloudy 

9 

5«       54 

65       57 

62       54 

70       71 

72      60 

63       50 

Rain 

10 

50       50 

54       54 

45       52 

70       55 

60      52 

38       45 

Cloudy  and  fair 

II 

45       47 

50      51 

Si       50 

65      54 

62      48 

33       38 

Fair  and  windy 

12 

45       SO 

49      SS 

50       54 

65      56 

63       55 

36      42 

Fair 

13 

48       SS 

54      60 

52      62 

71       55 

64       42 

45       62 

Fair 

14 

54       58 

50      64 

57       63 

70      62 

65       56 

52      63 

Cloudy 

IS 

46      50 

4«      52 

54       56 

61       62 

65      62 

38       43 

Cloudy  and  rainy 

16 

52       54 

56      58 

56      58 

75       79 

68      70 

50      52 

Rainy 

17 

50      50 

56       55 

54       56 

72       62 

68      60 

42      48 

Fair 

18 

19 

47       55 
SS       60 

50      6l 
58      68 

54      60 
58      68 

72       50 
71       59 

63       45 
66      49 

37       62 

42       67 

Fair 
Fair 

20 

58      63 

62      70 

58       72 

68      65 

63      55 

55       70 

Fair 

21 

58      65 

.62      69 

62       72 

67       71 

65      58 

49      68 

Fair 

22 

55      65 

61       70 

64      68 

68      65 

67      53 

48       70 

Fair 

23 

57      65 

62      71 

64        72 

74      62 

66      57 

50       73 

Fair 

24 
23 
26 

50      58 
47       55 
50       55 

56      62 
52       59 
55       58 

64       72 

62    60 

60     60 

59      46 
64      64 

63      44 
54       55 
56      62 

SO       73 
38       50 
34      46 

Fair  and  windy 
Fair  and  cloudy 
Cloudy  and  rainy 

•27 

23 

52       54 
57       58 

60      60 
62      62 

58      63 
60      55 

62      65 

72       75 

65       65 
70      70 

45       50 
46      45 

Cloudy 
Rainy  and  cloudy 

?9 

60       68 

62       62 

58       60 

75       74 

70       74 

SO       53 

Cloudy 

house  increased  the  moisture  reading  from  75  to  79 
degrees.  During  certain  rainy  and  damp  days,  the 
outside  air  is  more  moist  than  the  air  of  the  storage 
house.  To  ventilate  on  such  days  means  to  bring  in 


1 82  Diseases  of  Truck  Crops 

an  excess  of  moisture  and  not  to  ventilate  has  the  same 
result,  since  by  shutting  off  all  ventilation  the  inside 
moisture  will  accumulate.  Thus  on  days  when  the 
inside  air  is  moist,  natural  ventilation  is  insufficient. 
Hence  the  many  critical  periods  during  the  storage 
season. 

How  to  Meet  the  Ventilation  Problem  in  Storage. 
The  best  means  of  natural  ventilation  is  from  the 
sides,  either  through  doors  and  windows  or  through 
special  ventilators  (fig.  29  a-c).  The  bins  should  be 
constructed  with  false  slat -bottoms,  raised  from  three 
to  four  inches  from  the  floor;  the  sides  should  be 
slatted,  and  at  least  eight  inches  from  the  wall,  this 
space  being  connected  directly  with  the  opening  to 
the  floor  below. 

The  ventilation  between  the  floors  must  be  pro- 
vided by  means  of  trap-doors.  In  small  houses  with 
one  row  of  bins  on  each  floor,  these  ventilators  may  be 
12  to  1 6  inch  trap-doors  running  parallel  and  adjacent 
to  the  side  walls.  In  medium  sized  houses  with  two 
rows  of  bins  and  the  main  aisle  through  the  center 
running  lengthwise  through  the  house,  the  bins 
should  be  12  to  1 6  inches  from  the  wall  and  the  trap- 
door alongside  the  wall  should  occupy  the  distance 
between  the  wall  and  the  bin.  In  the  center  aisle, 
which  is  usually  three  feet  wide,  this  entire  walk 
could  well  be  converted  into  two  parallel  trap-doors, 
each  i%  feet  wide.  Large  houses  should  have  their 
main  aisle  along  the  side  walls.  These  should  be  at 
least  3>2  feet  wide.  A  center  aisle  between  the  two 
rows  of  bins  should  be  three  feet  wide.  All  these 


FIG.    29.     SWEET  POTATO  STORAGE  HOUSES. 

a.  An  ideal  large  commercial  dry  kiln  potato  house,  showing  windows  and  top 
ventilators,  b.  a  small  poor  potato  house  lacking  means  of  ventilation,  c.  a  close 
side  view  of  the  top  of  the  ventilator  shown  at  a. 


Family  Convolvulaceae  183 

aisles  should  be  converted  into  trap-doors  of  two  pairs, 
at  least  ijA  feet  wide,  opening  by  means  of  weights 
either  way  from  the  center,  and  occupying  the  entire 
length. 

A  series  of  roof  ventilators  should  be  provided, 
sufficient  to  carry  off  at  least  most  of  the  moisture. 
In  small  houses  there  should  be  at  least  two  such 
ventilators,  each  about  three  feet  square  and  about 
five  feet  high.  In  medium  sized  houses  there  should 
be  three  of  similar  dimensions.  In  large  houses 
from  four  to  six  ventilators  should  be  provided 
(fig.  29  a  and  c). 

Where  sweet  potatoes  are  stored  in  bins,  they 
should  first  be  put  into  every  other  one,  beginning 
with  the  lowest  and  finishing  with  the  top  floor. 
Thus  the  filled  bins  will  have  a  chance  to  dry  out. 
Bins  deeper  than  seven  feet  should  be  divided  by  two 
partitions,  leaving  a  two  or  three  inch  air  space 
between  them.  The  inner  bins  throughout  should  be 
filled  first.  It  is  a  mistake  to  close  doors  and  venti- 
lators when  the  potatoes  are  sweating,  for  during  this 
stage  all  the  ventilation  possible  should  be  given,  even 
at  night,  provided  of  course  that  the  temperature 
does  not  go  so  low  as  to  cause  chilling. 

Artificial  Aids  in  Storage.  Each  floor  should  be 
provided  with  an  accurate  recording  thermometer  and 
hygrometer.  With  the  help  of  these  two  instru- 
ments, the  critical  point  of  excess  heat  and  moisture 
may  be  easily  determined.  It  is  possible  that  in  order 
to  bridge  over  these  critical  periods  in  storage  some 
system  of  artificial  drying  may  be  required.  This 


184  Diseases  of  Truck  Crops 

may  be  accomplished  by  the  use  of  fans  or  blowers 
run  by  electricity  or  by  a  small  gasoline  motor. 

WEEDS 

There  are  but  few  weeds  in  this  family  which 
are  subject  to  the  same  diseases  as  the  sweet  potato. 
The  wild  morning-glory  (Ipomcea  pur  pur  ea),  the 
wild  sweet  potato  (Ipomosa  pandurata) ,  and  the 
small  and  great  bindweed  (Convolvulus  arvensis  and 
C.  sepium)  are  all  subject  to  black  rot,  Sph&ronema 
fimbriatum.  All  these  weeds  are  also  attacked  by 
white  rust,  Cystopus  ipomcece-pandurancB.  Whether 
this  rust  is  the  same  as  the  white  rust  of  the  sweet 
potato,  or  whether  it  is  another  physiological  species 
or  race,  still  remains  to  be  determined.  But  in  any 
case,  these  weeds  must  be  kept  out  of  sweet  potato 
fields  if  we  desire  to  keep  the  black  rot  of  sweet 
potato  in  check. 


CHAPTER  XIII 

FAMILY  CRUCIFER^E 

THIS  family  ranks  high  in  the  number  of  impor- 
tant cultivated  plants  that  it  contains.  Of  the 
truck  crops  of  economic  importance  may  be  men- 
tioned the  Brussels  sprouts,  cabbage,  cauliflower,  col- 
lard,  horseradish,  kale,  kohlrabi,  mustard,  radish, 
rutabaga,  sweede,  turnip,  and  watercress. 

According  to  the  Thirteenth  Census  of  the  United 
States,  the  area  devoted  to  cabbage  in  1909  in  all  the 
States  was  125,998  acres,  and  the  total  crop  was  val- 
ued at  $9,719,641.  The  important  cabbage  States, 
ranked  according  to  area,  were  as  follows :  New  York, 
Wisconsin,  Virginia,  Ohio,  Pennsylvania,  Illinois, 
New  Jersey,  Texas,  Michigan,  California,  Maryland, 
Florida,  Colorado,  Iowa,  Massachusetts,  Minne- 
sota, Louisiana,  South  Carolina,  Mississippi,  Ala- 
bama, Tennessee,  and  Kansas.  States  with  less  than 
1000  acres  are  omitted. 

The  total  area  of  cauliflower  in  1909  in  the  United 
States  was  estimated  at  3466  acres  and  the  total 
crop  was  valued  at  $602,885.  The  States  which 
produced  most  of  the  crops  are:  New  York,  Cali- 
fornia, Illinois,  Massachusetts,  and  Florida. 

185 


1 86  Diseases  of  Truck  Crops 

The  total  1909  area  in  horseradish  was  estimated  at 
1475  acres,  and  the  total  crop  valued  at  $233,885. 
The  crop  is  grown  mostly  in  North  Dakota,  Pennsyl- 
vania, New  York,  New  Jersey,  and  Illinois. 

The  total  1909  area  in  kale  was  estimated  at  1495 
acres,  and  the  total  crop  valued  at  $146,010.  The 
crop  is  principally  grown  in  Virginia,  Kentucky, 
Maryland,  and  New  York. 

The  total  1909  area  devoted  to  radish  was  esti- 
mated at  2269  acres,  and  the  total  crop  valued  at 
$293,062.  The  crop  is  grown  in  the  following  States, 
ranking  in  order  according  to  acreage:  New  York, 
Alabama,  Virginia,  Illinois,  Mississippi,  Louisiana, 
Missouri,  and  Texas. 

DISEASES  OF  CABBAGE  (Brassica  oleracea) 

The  cabbage,  although  a  hardy  plant,  is  neverthe- 
less subject  to  numerous  diseases.  Disease  may  re- 
duce the  profits  of  the  crop  by  fifty  per  cent.,  or  even 
mean  total  failure. 

CLUB  ROOT 
Caused  by  Plasmodiophora  brassicce  Wor. 

Club  root  is  a  field  disease  only.  Few  plant  dis- 
eases are  as  cosmopolitan  as  this  trouble.  It  is 
found  in  many  of  the  European  countries,  and  in 
Australia,  New  Zealand,  and  in  the  United  States. 
The  loss  from  club  root  ranges  from  forty  to  seventy 


FIG.  30.    CABBAGE  DISEASES. 

a.  Club  root  (after  Cunningham),  b.  cell  filled  with  spores  of  the  club  root  or- 
ganism, c.  spores  and  swarm  spores  of  Plasmodiophora  brassica  (b.  and  c.  after 
Chuff),  d.  black  rot  of  cabbage  (after  F.  C.  Stewart),  e.  individual  black  rot  germs  of 
Pseudomonas  campestris,  /.  black-leg  on  young  cabbage  seedling,  g.  black-leg  lesion 
on  foot  of  older  cabbage  plant,  h.  black-leg  lesion  on  cabbage  leaf,  i.  pycnidium  of 
Phoma  oleracecE,  j.  pycnospores  of  P.  oleracece  (i.  and.;',  after  Manns). 


.Family  Cruciferae  187 

per  cent,  of  the  crop,  although  most  of  it  may  be 
prevented. 

Symptoms.  Affected  plants  show  a  wilting  of  the 
foliage  in  the  day,  although  recovering  in  the  even- 
ing or  during  cloudy  weather.  Diseased  plants  are 
dwarfed,  pale,  and  sickly  looking.  The  seat  of  the 
trouble  is  at  the  roots.  The  latter  swell  considerably 
in  size,  often  taking  on  the  form  of  a  hernia  (fig.  30  a). 
The  disease  is  more  severe  on  seedlings  in  the  seed 
bed,  from  whence  it  is  carried  to  the  field. 

The  Organism.  Club  root  is  caused  by  a  slime  mold. 
The  spores  of  the  parasite  (fig.  30  b)  are  nearly  round 
and  ^possess  a  transparent  and  refractive  cell  wall. 
According  to  Chupp,1  the  first  signs  of  germination 
are  a  swelling  of  the  spores,  followed  later  by 
a  bulging  at  one  side.  The  inner  pressure  exerted 
splits  the  spore  wall,  thus  permitting  the  protoplasm 
(swarm  spores)  to  ooze  out.  The  latter  is  with- 
out a  cell  wall  (fig.  30  c) ,  and  is  capable  of  motion  by 
means  of  a  thick  flagellum  at  the  small  end.  The 
germination  of  the  spores  is  improved  by  exposing 
them  for  a  short  time  to  cold  and  drying.  The  best 
medium  is  water  which  has  been  filtered  through 
muck  soil. 

Infection  of  the  host  takes  place  through  the  wall 
of  the  root  hair  while  the  organism  is  in  a  uninucleate 
stage.  Entrance  of  the  parasite  is  evidenced  by  the 
browning  and  shriveling  of  the  root  hair.  The  dis- 
ease does  not  seem  to  be  spread  from  place  to  place 

1  Chupp,  Charles,  New  York  (Cornell)  Agr.  Expt.  Sta.  Bul.t 
387:421-452,  1917. 


1 88  Diseases  of  Truck  Crops 

by  the  wind.  But  infected  manure  in  the  seed  bed 
will  result  in  infected  seedlings  carrying  the  disease 
into  a  new  field.  Club  root  is  known  to  attack  a 
large  number  of  cruciferous  hosts,  the  more  suscepti- 
ble of  which  include  all  of  the  cultivated  species. 

Control.  The  best  method  of  controlling  club  root 
is  to  grow  cabbage  on  new  land,  or  on  land  that 
was  rotated  with  other  crops,  and  given  a  rest  from 
cruciferous  crops  for  some  time.  Where  it  is  not 
possible  to  do  this,  infected  fields  should  be  limed. 
Table  15,  adapted  from  Cunningham,1  clearly  shows 
the  effect  of  lime  in  controlling  club  root. 

From  Table  15,  it  is  seen  that  the  use  of  fresh  or 
air-slaked  lime  lowers  the  percentage  of  club  root  as 
compared  with  the  calcium  chloride  on  check  plats. 
Moreover,  when  clubbing  appeared  in  the  limed 
areas,  the  disease  seemed  to  be  confined  to  the  lowest 
roots  and  outside  of  the  reach  of  lime.  This  then 
enabled  the  affected  plants  to  make  a  crop  in  spite  of 
the  disease.  The  best  effect  of  liming  may  be  ex- 
pected when  the  lime  is  thoroughly  incorporated  in 
the  soil  to  a  depth  of  six  to  nine  inches.  As  far  as 
possible  the  trucker  should  avoid  susceptible  varieties 
of  cabbage,  among  which  may  be  mentioned :  Mam- 
moth Rock  Red,  Dark  Red  Erfurt,  American  Savoy, 
Perfection  Savoy,  All  Seasons,  and  Volga.  Of  the 
more  resistant  varieties  of  cabbage  may  be  mentioned 
Hollander,  Stone  Mason,  Large  Late  Flat  Dutch, 
and  Henderson's  Early  Summer.  Finally,  care 

1  Cunningham,  L.  C.,  Vermont  Agr.  Expt.  Sta.  Bui.,  185  :  67-96, 
1914. 


Family  Cruciferae 


189 


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190  Diseases  of  Truck  Crops 

should  be  taken  to  exclude  club  roots  from  the  seed 
bed,  since  many  an  outbreak  of  this  trouble  may  be 
traced  back  to  the  use  of  previously  infected  seedlings. 

BLACK  ROT 

Caused    by   Pseudomonas   campestris    (Pammel) 
Ew.  Sm. 

The  disease  is  known  to  growers  as  stem  rot  and 
black  rot.  The  latter  perhaps  is  the  more  common 
name.  The  trouble  may  now  be  found  wherever 
cabbage  is  grown  on  a  large  scale. 

Symptoms.  Black  rot  has  distinct  symptoms 
which  cannot  easily  be  confused  with  other  cabbage 
diseases.  On  the  leaves,  the  symptoms  are  mani- 
fested as  a  burning  appearance  on  the  edges  (fig. 
30  d)  and  a  yellowing  of  all  the  affected  parts  except 
the  veins,  which,  remain  blackened.  From  the  mar- 
gin of  the  leaves  the  disease  works  downwards  to  the 
stalk.  From  there  the  disease  travels  up  again  to 
the  leaves  and  from  there  to  the  stems.  The  parasite 
works  in  the  fibro-vascular  bundles  of  the  leaves  and 
main  stalk,  causing  a  premature  defoliation.  Occa- 
sionally, the  disease  enters  one  side  of  the  stalk,  the 
latter  becoming  dwarfed  and  the  cabbage  head  be- 
coming one  sided.  In  severe  cases  of  attack,  there  is 
a  total  lack  of  head  formation.  In  splitting  open  a 
stump  of  an  affected  plant,  we  will  find  a  black  ring 
which  would  correspond  to  the  places  of  the  fibro- 
vascular  bundles  invaded  by  the  organism.  Smith1 

1  Smith,  E.  F.,  U.  S,  Dept.  of  Agr.  Farmers  Bui.,  68:  5-21,  1898. 


Family  Cruciferae  191 

found  that  the  infection  takes  place  through  small 
openings  naturally  found  on  the  leaves  and  known  as 
water  pores  which  are  found  scattered  over  the  teeth 
of  the  leaves.  '  Infection  by  means  of  insect  bites  is 
also  a  very  common  occurrence.  Outbreaks  of  black 
rot  in  new  fields  may  undoubtedly  be  traced  back 
to  the  use  of  infected  manure.  Black  rot  also  at- 
tacks broccoli,  Brussels  sprouts,  cauliflower,  char- 
lock, collard,  kale,  kohlrabi,  black  mustard,  rape, 
rutabaga,  radish,  sweede,  and  turnip. 

The  Organism.  Pseudomonas  campestris  is  a  rod- 
shaped  organism,  slightly  longer  than  it  is  broad. 
When  young  it  is  actively  motile  by  means  of  long 
polar  flagella  (fig.  30  e).  It  is  found  single  or  in  pairs 
and  produces  no  spores.  It  liquefies  gelatine  com- 
pletely in  about  fifteen  days.  On  agar  plates  the  col- 
onies are  round,  yellow  in  color,  and  the  margin  entire. 
On  potatoes  a  copious  growth  is  produced  with 
no  odor  and  no  browning  of  substances.  The  in- 
vestigations of  Harding1  and  others  have  proved 
that  the  black  rot  germ  may  be  introduced  into  the 
seed  bed  and  into  new  fields  from  infected  cabbage 
patches.  The  virulence  of  black  rot  is  largely  de- 
pendent on  the  weather.  It  is  unfortunate  that 
favorable  weather  conditions  for  the  cabbage  plants 
are  also  favorable  for  the  disease. 

Control.  Before  planting,  cabbage  seed  should  be 
disinfected  for  fifteen  minutes  in  a  solution  of  ]^  pint 
of  pure  (40%)  formaldehyde  diluted  in  seven  gallons 

1  Harding,  H.  A.,  New  York  (Geneva)  Agr.  Expt.  Sta.  Bui., 
251: 178-194,  1904. 


192  Diseases  of  Truck  Crops 

of  water.  In  making  the  seed  bed,  manure  known  to 
be  free  from  cabbage  refuse  should  be  used.  All  insect 
pests  should  be  kept  in  check  by  spraying,  and  no 
animals  should  be  allowed  to  roam  in  sick  patches. 
Insects  and  farm  animals  act  as  carriers  of  black 
rot.  The  disease  cannot  be  controlled  by  merely 
cutting  off  diseased  foliage.  If  anything,  this 
operation  aggravates  the  trouble.  Diseased  plants 
should  be  pulled  out  and  destroyed.  Crop  rotation 
should  be  practiced  wherever  the  disease  is  well 
established. 

SOFT  ROT 
Caused  by  Bacillus  carotovorus  Jones. 

Soft  rot,  although  a  field  trouble,  causes  great 
damage  to  stored  cabbage.  The  greatest  losses 
are  reported  from  New  York  and  Wisconsin  where 
cabbage  is  stored  on  a  large  scale. 

Symptoms.  The  disease  is  characterized  by  a  soft, 
mushy  to  slimy  decay  of  the  entire  plant.  The  dis- 
ease works  very  rapidly  under  favorable  conditions 
of  moisture  and  temperature.  The  causal  organism 
can  gain  entrance  only  through  a  wound  or  bruise. 
Rough  handling  of  the  crop  during  hauling  and  stor- 
ing therefore  opens  the  way  to  heavy  infection  and 
consequently  loss  from  soft  rot. 

1  The  Organism.  The  Bacillus  is  rod- shaped,  long 
or  short,  and  usually  formed  in  chains.  It  moves 
about  by  peritrichous  flagella.  It  completely  lique- 


Family  Cruciferae  193 

fies  gelatine  in  about  six  days.     Gas  is  produced  with 
a  majority  of  strains. 

Control.  The  greatest  loss  in  storage  occurs  where 
the  temperature  is  maintained  much  above  the  freez- 
ing point  and  where  the  facilities  for  ventilation  are 
poor.  To  remedy  this,  the  temperature,  as  far  as  possi- 
ble, should  be  maintained  one  or  two  degrees  above 
freezing .  The  crop  should  be  thoroughly  dried  and  ex- 
posed to  the  sunlight  before  being  entered  into  storage. 
Diseased  fields  should  be  rotated  to  other  crops. 

DAMPING  OFF 
Caused  by  Olpidium  brassicce  (Worr.)  Dang. 

The  symptoms  of  damping  off  are  similar  to  those 
produced  by  Pythium  de  Baryanum,  p.  43.  The 
sporangia  of  the  parasite  may  be  found  singly  or 
in  groups  in  each  infected  host  cell.  The  zoospores 
are  globose,  uniciliate.  The  resting  spores  are 
globose,  wrinkled,  and  star-like  in  appearance. 

The  disease  is  found  mostly  in  seed  beds,  where  it 
does  considerable  damage.  For  methods  of  control 
see  p.  43. 

WHITE  RUST 
Caused  by  Cystopus  candidus  (Pers.)  Lev. 

White  rust  of  cabbage  is  seldom  troublesome 
enough  to  attract  attention.  The  symptoms  of  the 
disease  are  the  same  as  on  other  cruciferous  hosts 
such  as  mustard  or  radish,  p.  211. 

13 


194  Diseases  of  Truck  Crops 

DOWNY  MILDEW 
Caused  by  Peronospora  parasitica  (Pers.)  De  By. 

Downy  mildew,  while  a  common  field  disease, 
causes  considerable  damage  to  young  seedlings. 
It  is  characterized  by  whitish  downy  patches  on  the 
under  side  of  the  leaf.  Seen  from  above,  the  af- 
fected areas  are  angular,  pale  yellow,  and  somewhat 
shrunken.  The  spots  seem  to  be  limited  by  the 
veins  of  the  leaf.  The  disease  is  common  in  damp 
weather.  Besides  the  cabbage,  cauliflower,  radish, 
turnips,  and  numerous  other  cruciferous  hosts  are 
known  to  be  susceptible  to  downy  mildew. 

The  sporophores  of  the  fungus  are  stout  and 
numerously  branched,  each  branch  repeatedly  forked. 
The  tips  of  the  smaller  branches  are  slender  and 
curved.  The  conidia  are  broadly  elliptical,  and  the 
resting  spores  are  globose  and  smooth,  becoming 
wrinkled  with  age. 

In  the  seed  bed  or  in  the  field,  spraying  with 
4-4-50  Bordeaux  will  control  the  disease.  The  first 
application  should  be  given  as  soon  as  the  disease 
makes  its  appearance.  Later  the  application  will 
be  governed  by  weather  conditions. 

DROP 
Caused  by  Sclerotinia  libertiana  Fckl. 

Drop  is  a  disease  fairly  common  on  cabbage.  The 
trouble  may  be  recognized  by  a  drooping  and  wilting 


Family  Cruciferae  195 

of  the  leaves.  The  bases  of  the  affected  foliage  are 
covered  with  a  white  weft  of  mycelial  growth,  later 
by  sclerotia.  For  a  more  extended  discussion  of  the 
disease  see  lettuce  drop,  p.  143. 

BLACK  LEG  OR  FOOT  ROT 
Caused  by  Phoma  oleracea  Sacc. 

Black  leg,  first  noticed  in  the  United  States  by 
Manns1  in  Ohio,  was  undoubtedly  introduced  here 
from  Europe. 

Symptoms.  The  disease  is  usually  manifested  in 
the  seed  bed  about  two  to  three  weeks  before  trans- 
planting in  the  field.  The  trouble  at  first  appears 
as  white  elongated  sunken  lesions  on  the  stem  and 
below  the  leaf  attachment  (fig.  30  f ) .  Scattered  over 
the  lesions  are  minute  black  specks  which  constitute 
the  pycnidia  or  fruiting  sacs  of  the  fungus  (fig.  30  i 
and  j).  Infected  seedlings  usually  collapse  and  take 
on  a  bluish  color.  In  the  field,  the  foliage  of  the 
older  but  affected  plants  (fig.  30  h)  usually  take  on  a 
mottled,  metallic,  bluish-red  color  at  the  margins, 
and  the  lower  outer  leaves  wilt.  On  examining  such 
plants  there  will  always  be  found  sunken  lesions 
(fig.  30  g)  which  often  girdle  the  foot  of  the  plant. 
In  wet  weather  affected  plants  attempt  to  produce 
new  roots  above  the  infected  area,  which,  however, 
are  never  able  sufficiently  to  support  the  plant. 
Foot  rot  is  often  confused  with  forms  of  injury 
brought  about  by  maggots. 

1  Manns,  T.  P.,  Ohio  Agr.  Expt.  Sta.  Bui.,  228:  255-297,  1911. 


196  Diseases  of  Truck  Crops 

Treatment.  Manns  recommends  treatment  of  the 
seed  bed  with  4-4-50  Bordeaux  to  be  applied  im- 
mediately after  planting,  at  the  rate  of  one  gallon  to 
each  ten  square  feet  of  bed  space.  The  bed  is  again 
sprayed  with  Bordeaux  about  two  weeks  before  and 
once  again  at  transplanting. 

BLACK  MOLD 
Caused  by  Alternaria  brassica  (Berk.)  Sacc. 

Black  mold  is  a  serious  disease  of  the  cabbage  in 
the  Southern  States.  It  also  attacks  collards. 

Symptoms.  Affected  leaves  are  covered  with 
spots  which  are  nearly  black  on  the  under  side  of  the 
leaf.  The  spots  are  composed  of  a  series  of  rings, 
the  smaller  ones  enclosed  within  the  larger  (fig.  31  a). 
There  is  no  distinct  border  separating  the  diseased 
from  the  healthy,  the  spots  gradually  shading  off 
into  the  healthy  tissue.  Little  is  known  of  the  causa- 
tive fungus  or  of  the  control  of  this  disease.  It  is 
probable  that  spraying  with  4-4-50  Bordeaux  will 
be  of  value. 

LEAF  SPOT 
Caused  by  Cercospora  bloxami  B.  and  Br. 

Leaf  spot  is  of  little  economic  importance.  It  only 
attacks  the  leaves  of  weak  or  languid  plants.  The 
spots  are  pale,  somewhat  circular,  surrounded  by  a 
slightly  raised,  faintly  purple  border.  The  conidial 


FIG.  3i.     CABBAGE  DISEASES. 

a.  Alternaria  black  mold,  6.  cabbage  seedlings  growing  in  a  cabbage  sick  soil 
which  has  been  steam  sterilized,  c.  sick  cabbage  seedlings  in  a  cabbage  sick  soil, 
(after  Jones  and  Oilman) ,  d.  an  old  wilt  infected  cabbage  plant:  notice  bare  stalk, 
e.  conidia  of  Fusarium  conglulinans,  f.  clamydospores  (resting  spores),  of  F.  con- 
glutinans,  g.  wilt  infected  cabbage  seedlings:  notice  how  the  leaflets  drop  off  as  a 
result  of  the  disease. 


Family  Cruciferae  197 

tufts  are  prevalent  in  the  center  of  the  spots,  and  are 
pale  brown  and  sparingly  septate.  The  conidia  are 
long  clavate,  tapering,  straight  to  curved,  many  sep- 
tate, and  hyaline  to  faint  smoky  color. 

WILT  OR  YELLOWS 
Caused  by  Fusarium  conglutinans  Woll. 

There  is  no  other  cabbage  disease  that  is  economi- 
cally so  important  as  wilt.  This  trouble  is  threaten- 
ing the  cabbage  industry  in  many  parts  of  the  United 
States.  In  the  cabbage  centers  of  Ohio  and  Wiscon- 
sin, truckers  lose  so  heavily  from  wilt,  that  in  many 
sections,  the  growing  of  the  crop  has  been  made  very 
unprofitable. 

Symptoms.  The  term  * '  yellows ' '  well  describes  the 
disease.  Affected  seedlings  are  yellowish  and  stunted 
in  growth  with  a  tendency  to  drop  their  lower  leaves 
at  the  least  touch  (fig.  31  g).  Such  plants  when 
transplanted  in  the  field  either  die  outright  or  make 
very  slow  growth.  The  symptoms  in  the  older 
affected  plants  are  the  same  as  on  the  seedlings. 
The  outer  leaves  turn  yellow  and  drop  off  one  by  one, 
until  a  bare  stump  and  top  head  are  left  (fig.  31  d). 
Usually  the  plant  is  uniformly  attacked;  but  the  in- 
fection may  be  confined  to  one  side.  This  one-sided 
check  results  in  the  lateral  warping  and  curving  of 
the  stems  and  leaves.  Under  field  conditions,  high 
temperatures  are  very  favorable  for  the  spread  and 
development  of  yellows. 

The  Organism.    The  best  description  of  Fusarium 


198  Diseases  of  Truck  Crops 

conglutinans  Woll.  is  given  by  Gilman.1  Sporo- 
dochia,  lacking  or  greatly  reduced,  pionnotes  never 
present,  conidia  borne  on  short  conidiophores  strewn 
throughout  the  mycelium.  The  majority  of  spores 
are  non-septate,  a  few  are  one  to  three  septate 
(fig.  31  e) ;  conidia  with  higher  septation  are  rare. 
In  old  cultures,  chlamydospores  are  produced  in 
great  abundance  (fig.  31  f). 

Control.  Cabbage  yellows  cannot  be  readily 
controlled.  Naturally  a  clean  seed  bed  should  be 
chosen  (fig.  31  b-c).  However,  the  healthy  seedlings 
when  transplanted  into  infected  fields  will  soon  con- 
tract the  disease.  The  same  also  holds  true  even 
when  the  seeds  are  disinfected.  Neither  is  crop 
rotation  a  sure  method  of  control.  It  is  doubtful  if 
fifteen  years'  rest  from  cabbage  will  free  a  soil  from 
the  causative  parasite.  The  best  method  of  control 
is  the  development  of  resistant  varieties.  This  has 
already  been  accomplished  by  Jones  and  Gilman2 
who  selected  a  strain  from  the  Hollander  which 
they  named  Wisconsin  Hollander  No.  8.  This  strain 
is  said  to  be  nearly  100  per  cent,  resistant  to  wilt.  The 
same  is  also  true  for  the  Volga  (fig.  32  a-b).  The 
question  arises  as  to  whether  a  cabbage  selected  for 
resistance  under  Wisconsin  soil  will  show  it  in  a  like 
degree  in  other  climatic  conditions  and  soil.  For 
the  cabbage  the  answer  may  be  given  in  the  affirma- 
tive. For  instance,  the  Houser  and  the  Volga,  which 

1  Oilman,  J.  C.f  Annals  Missouri  Bot.  Garden,  3  : 2-84,  1916. 

2  Jones,  L.  R.,  and  Gilman,  J.  C.,  Wisconsin  Agr.  Expt.  Sta.  Bui., 
38  : 1-69,  1915. 


FIG.  32.     CABBAGE  DISEASES. 

a.  Two  rows  of  Volga,  a  highly  resistant  commercial  cabbage  growing  in  a 
cabbage  sick  soil  (yellows),  b.  resistant  cabbage  strains  in  a  cabbage  sick  soil 
(a.  and  b.  after  Jones  and  Oilman). 


Family  Cruciferae  199 

have  proved  wilt  proof  in  Maryland,  have  proven 
equally  resistant  under  Wisconsin  conditions.  It  is, 
however,  advisable  to  grow  seed  in  the  same  locality 
where  the  resistant  cabbage  has  been  developed. 
The  method  of  developing  resistant  varieties  is 
given  more  fully  on  p.  374. 

ROOT  KNOT 
Caused  by  Heterodera  radicicola  (Greef)  Mull. 

Root  knot  is  very  widespread  in  the  Southern 
States,  but  is  confined  mostly  to  the  light  sandy  soils. 
It  is  often  mistaken  for  club  root.  Careful  observa- 
tion will  show  the  differences.  Root  knot  is  char- 
acterized by  small  swellings  on  the  lateral  feeding 
roots.  For  a  description  of  the  parasite  and  meth- 
ods of  control  see  p.  49. 

DECAY  OF  CABBAGE  IN  STORAGE 

Not  all  field-grown  cabbage  is  consumed  when 
harvested.  A  large  part  of  the  crop  is  stored  away 
for  winter  use.  It  is  estimated  by  Harter1  that  of 
the  thousands  of  tons  stored  every  fall,  from  10  to 
50  per  cent,  is  annually  lost  from  decay.  With 
the  exception  of  yellows,  practically  all  the  other 
field  rots  of  cabbage  may  be  active  also  under  storage 
conditions.  Therefore,  to  store  a  clean  crop  we 
must  produce  a  clean  crop  in  the  field  and  on  no 
account  should  infected  cabbage  be  allowed  in  the 

1  Harter,  L.  L.,  U.  S.  Dept.  Agr.'Bur.  PI.  Ind.  Circ.,  39: 3-8,  1909. 


2oo  Diseases  of  Truck  Crops 

storage  house.  Cabbage  from  badly  diseased  plants 
should  be  disposed  of  early. 

Poor  Storage  Conditions.  Cabbage  houses  are 
usually  built  as  permanent  structures.  When  this 
is  the  case,  they  must  be  thoroughly  cleaned  out  and 
disinfected  every  year  before  storing  a  fresh  crop. 
All  indoor  framework  should  be  sprayed  with  a  solu- 
tion of  one  pint  of  formaldehyde  in  forty  gallons  of 
water.  This  is  done  a  week  or  two  before  storing  in 
order  to  allow  the  house  to  dry  thoroughly. 

In  harvesting  and  handling  the  crop,  every  care 
should  be  taken  to  prevent  unnecessary  bruising  of 
the  heads.  Storers  of  cabbage  are  confronted  with 
the  same  difficulties  as  storers  of  sweet  potatoes. 
With  both,  the  great  problem  is  the  ventilation  and 
the  elimination  of  excess  of  moisture  given  off  by  the 
crop  in  storage.  In  warm  houses  quantities  of  mois- 
ture soon  accumulate  in  the  house,  which,  if  not 
carried  off,  soon  deposit  on  the  cabbage. 

Storage  houses  may  be  so  constructed  as  to  take 
care  of  the  ventilation  and  moisture  under  normal 
conditions.  The  walls  of  the  buildings  should  pro- 
vide a  dead  air  space  to  prevent  the  penetration  of 
the  outdoor  moisture.  With  brick  walls,  two  four- 
inch  walls  could  be  laid  and  tied  up  by  a  header 
course,  thus  providing  an  air  space  of  two  to  three 
inches  between  them.  Wherever  possible  thick 
walls  should  be  preferred,  as  these  make  it  possible 
to  keep  the  interior  cool  during  hot  weather.  The 
roof  should  be  provided  with  a  good  outer  covering 
of  shingles,  and  with  an  inner  lining  so  built  as  to 


Family  Cruciferae  201 

provide  a  dead  air  space.  If  the  inner  lining  is  made 
up  of  lumber,  the  boards  should  run  parallel  with  the 
rafters,  rather  than  at  right  angles  to  them,  so  that 
any  condensed  water  may  run  off  to  the  eaves  rather 
than  fall  from  each  joint.  Ventilation  should  be 
encouraged  by  means  of  top  ventilators  on  the  roof. 
These  should  be  provided  with  dampers,  manipulated 
and  controlled  by  ropes  extending  to  the  passage- 
way. Small  windows  installed  above  the  foundation 
line  in  the  walls  will  admit  air  from  below  and  induce 
a  better  circulation.  The  windows  may  be  screened 
with  an  iron  netting  in  order  to  keep  out  mice. 

There  are  two  ways  of  storing  cabbage — in  bins  or 
on  shelves.  The  latter  is  preferred  because  there  is 
less  bulk  to  undergo  a  sweat,  and  each  individual 
cabbage  being  exposed  to  more  air  prevents  rotting. 
In  storing,  the  cabbage  should  be  placed  with  the 
stem  end  upward  so  that  all  possible  moisture  may 
readily  run  off  and  not  be  caught  and  held  by  the 
head  leaves. 

So  far  as  possible,  the  temperature  of  the  storage 
house  should  be  maintained  at  about  thirty-four 
degrees  F.  throughout  the  storage  period.  As  soon 
as  the  house  is  filled,  it  should  be  kept  closed  during 
the  day  and  be  opened  at  night  in  order  to  benefit 
from  the  cool  outdoor  air.  During  extremes  of  cold 
weather,  ventilation  should  be  reduced  to  a  minimum 
and  the  house  kept  warm  by  an  oil  heater  to  prevent 
freezing  of  the  cabbage.  The  Danish  Ball  Head, 
from  imported  seed,  seems  to  be  an  ideal  cabbage  for 
storage. 


202  Diseases  of  Truck  Crops 

DISEASES  OF  THE  CAULIFLOWER  (Brassica 
oleracea  var.  botrytis) 

The  cauliflower  with  few  exceptions  is  subject  to 
the  same  diseases  as  the  cabbage.  For  a  discussion 
of  black  rot,  see  p.  190;  soft  rot,  p.  192,  club  root, 
p.  1 86,  and  drop,  p.  143. 

BACTERIAL  LEAF  SPOT 
Caused  by  Pseudomonas  maculicola  McC. 

Bacterial  leaf  spot  was  first  studied  and  described 
by  McCulloch1  who  found  it  to  be  prevalent  in  south- 
eastern Virginia  and  in  Florida.  The  disease  un- 
doubtedly must  have  a  wider  and  more  geographical 
distribution  than  is  generally  known.  The  author 
has  met  with  this  disease  in  New  Jersey,  Delaware, 
Maryland,  and  Texas. 

Symptoms.  The  disease  is  characterized  by  numer- 
ous small  brownish  to  purple-gray  spots  (fig.  33  a). 
When  the  small  spots  coalesce,  the  entire  leaf  surface 
may  be  involved.  Practically  all  parts  of  the  leaves 
are  affected.  When  the  midribs  and  veins  are  at- 
tacked, the  tissue  becomes  shrunken,  and  the  leaves 
have  a  puckered  appearance.  In  early  stages  of 
infection,  the  spots  on  the  leaves  are  watersoaked, 
later  becoming  dry  and  dark  to  purplish  gray.  In 
transmitted  light  the  centers  of  the  spots  are  thin, 
almost  colorless,  and  surrounded  by  a  dark  border. 

1  McCulloch,  Lucia,  U.  S.  Dept.  of  Agr.  Bur.  PI.  lad.  Bui.  225  :  7- 
15,  1911. 


FIG.  33.     DISEASES  OF  THE  CAULIFLOWER  AND  RADISH. 

a.  Spot  disease  of  cauliflower  (after  McCulloch),  b.  white  rust  of  radish,  c.  conidio- 
phore  of  the  white  rust  fungus,  Cystopus  candidus,  d.  fertilization  in  Albugo  Candida, 
e.  germination  of  the  oospore  of  Albugo  Candida,  f.  ring  spot  on  cauliflower  head,  g. 
perithecium  of  Mycosphcerella  brassicicola,  h.  ascus  of  Mycosphcerclla  brassicicola,  i. 
ascospores  of  Mycosphcerella  brassicicola  (g.  to  ».  after  Osmun  and  Anderson). 


Family  Cruciferae  203 

The  diseased  leaves  become  yellow  and  drop  off 
prematurely.  The  trouble  apparently  does  not  at- 
tack the  cauliflower  head.  The  same  disease  may 
also  attack  cabbage,  but  not  radish,  rutabaga  turnip, 
or  mustard. 

The  Organism.  Pseudomonas  maculicola  is  a 
rod-shaped  organism,  with  rounded  ends,  usually 
forming  long  chains  in  certain  media,  but  producing 
no  spores.  The  organism  is  actively  motile  by  means 
of  polar  flagella.  Involution  forms  are  produced  in 
alkaline  beef  bouillon;  and  pseudo-zoogloese  occur 
in  acid  beef  bouillon.  No  gas  is  produced  and  the 
organism  is  aerobic,  and  is  killed  by  drying  and 
exposure  to  light. 

Control.  Badly  diseased  plants  should  be  pulled 
up  and  destroyed.  Spraying  with  4-4-50  Bordeaux 
is  recommended.  In  spraying  cauliflower  with 
copper  compounds,  and  especially  if  the  latter  are 
in  a  concentration  somewhat  stronger  than  the  plant 
can  stand,  numerous  warts  will  appear  on  the  leaves 
in  about  three  days  after  spraying.  These  warts 
should  not  be  mistaken  for  a  disease  induced  by  a 
parasitic  organism.  The  wart  formation  is  appar- 
ently due  to  a  stimulation  by  the  salts  absorbed  by  the 
host  cells.  Von  Schrenk x  found  that  warts  on  cauli- 
flower leaves  may  be  readily  produced  by  spraying 
them  with  a  solution  made  up  of  5  oz.  copper  car- 
bonate dissolved  in  a  mixture  of  three  pints  of  am- 
monia to  fifty  gallons  of  water.  He  further  found 

1  Von  Schrenk,  H.,  Missouri  Bot.  Gard.,  i6th  Ann.  Rept.  :  125, 
1905. 


204  Diseases  of  Truck  Crops 

that  leaf  warts  may  be  produced  by  spraying  with 
weak  solutions  of  copper  chloride,  copper  acetate, 
copper  nitrate,  and  copper  sulphate. 

RING  SPOT 
Caused  by  Mycosphczrella  brassicola  (Duby)  Lind. 

The  exact  distribution  of  this  disease  is  as  yet  un- 
known. The  trouble  was  studied  by  Osmun  and 
Anderson1  on  cauliflowers  shipped  from  California 
to  Boston. 

Symptoms.  On  the  leaves,  the  disease  appears  as 
numerous  small  spots  and  the  affected  foliage  turns 
yellow.  Most  of  the  spots  are  formed  on  the  laminae, 
but  others  are  also  formed  on  the  large  midribs. 
The  spots  are  definite  in  outline,  round  and  visible 
on  both  surfaces  of  the  leaf  (fig.  33  f).  The  color  is 
light  brown  to  gray,  with  dry  centers  surrounded  by 
olive  green  or  blue  green  borders  which  shade  off  in 
the  natural  color  of  the  leaf.  The  outer  edge  of  the 
spot  is  covered  with  the  fruit  of  the  fungus  (fig.  33 
g-i).  Ring  spot  also  attacks  the  cabbage.  Spray- 
ing with  4-4-50  Bordeaux  is  recommended. 

DISEASES  OF  THE  HORSERADISH  (Cochkaria 
armoracia) 

The  horseradish  is  generally  considered  a  hardy 

plant.     However,  it  is  subject  to  numerous  diseases. 

1  Osmun,  A.  V.,  and  Anderson,  P.  G.,  Phytopath.  5:  260-265,1915. 


Family  Cruciferae  205 

The  black  rot,  Pseudomonas  campestris,  is  the  same 
as  that  of  the  cabbage,  p.  190,  and  the  white  rust, 
Cystopus  candidus,  is  the  same  as  that  of  the  mus- 
tard, p.  211. 

ROOT  ROT 

Caused  by  Thielavia  basicola  (B.  and  Br.)  Zopf. 

Root  rot  of  horseradish  is  of  little  economic  im- 
portance. The  disease  is  confined  to  the  roots  of  the 
plant.  In  advanced  stages  the  normal  root  system 
may  be  entirely  lacking,  leaving  a  charred,  blackened 
stub.  New  roots  are  constantly  formed  above  the 
diseased  area,  but  these  in  turn  become  affected 
and  die.  It  is  these  new  roots  which  the  plant 
attempts  to  produce  that  manage  to  keep  the 
infected  host  alive  in  a  stunted  and  useless  form. 
For  a  description  of  the  organism  and  methods  of 
control,  see  p.  275. 

ASCOCHYTA  LEAF  SPOT 
Caused  by  Ascochyta  armor aci<R  Fckl. 

This  form  of  leaf  spot  is  rather  scarce  in  the  United 
States  and  may  be  easily  overlooked.  The  disease 
is  manifested  as  brownish  leaf  spots  of  various  sizes. 
Within  the  spots  numerous  pycnidia  are  formed 
which  bear  numerous  elliptic-oblong,  hyaline  one- 
septate  spores. 


206  Diseases  of  Truck  Crops 

SHOT  HOLE 
Caused  by  Septoria  armoracice,  Sacc. 

Shot  hole  is  a  very  serious  disease  which  attacks 
the  foliage  of  horseradish.  Diseased  leaves  turn 
yellow  and  become  peppered  with  round  spots, 
whitish  in  the  center,  surrounded  by  a  pale  yellow 
border.  The  spots  drop  out  and  give  the  leaves 
a  ragged  shaggy  appearance.  The  pycnidia  of  the 
fungus  are  formed  in  the  center  of  the  spots  previous 
to  their  dropping  out  or  on  the  remaining  margin 
of  the  spot. 

MACROSPORIUM  BLACK  MOLD 
Caused  by  Macrosporium  herculeum  E.  and  M. 

This  mold  is  confined  to  the  leaves  only.  Late 
in  the  summer  the  leaves  are  attacked  by  round 
spots  which  at  first  are  whitish,  and  later  become 
coated  with  a  black  mold  made  up  of  the  spore  bodies 
of  the  fungus.  Horseradish  may  also  be  attacked 
by  another  form  of  black  mold,  Alternaria  brassica 
(Berk.)  Sacc.,  see  p.  196. 

WHITE  MOLD 
Caused  by  Ramularia  armor  acicB  Fckl. 

White  mold  is  frequently  met  with  on  foliage  of 
the  horseradish.  The  spots  are  indefinite,  irregular, 


PIG.  34.     CERCOSPORA  LEAF  SPOT 
OF  HORSE  RADISH. 


Family  Cruciferae  207 

and  usually  occupy  large  areas  of  the  leaf.  At  first 
they  are  yellowish  red  in  color;  but  they  become  gray 
with  age. 

LEAF  SPOT 
Caused  by  Cercospora  armoracicB  Sacc. 

Leaf  spot  is  characterized  by  pale  spots  on  the 
leaves  (fig.  34).  The  spots  are  usually  confined  to 
weakened  leaves.  The  disease  is  of  no  importance. 

Control.  Usually  the  diseases  of  the  horseradish 
are  not  serious  enough  to  warrant  treatment.  How- 
ever, when  the  crop  is  grown  on  a  large  scale,  it 
should  not  be  planted  anywhere  near  cabbage  or 
other  cruciferous  plants  in  order  to  protect  it  from 
black  rot.  If  any  of  the  leaf  spots  become  serious 
the  affected  parts  may  be  removed  and  destroyed 
and  the  plants  sprayed  with  4-4-50  Bordeaux. 
The  plants  should  be  carefully  cultivated  and 
fertilized  in  order  to  maintain  their  vigor,  thereby 
also  preventing  the  leaf  diseases  from  getting 
troublesome. 

DISEASES  OF  THE  KALE  (Brassica  okracea 
var.  acephala) 

Kale  is  considered  a  very  hardy  plant ;  it  is,  however, 
subject  to  black  rot,  Pseudomonas  campestris  (Pam.) 
Ew.  Sm.  On  the  leaves,  black  rot  is  characterized 
by  dark  discoloration  of  the  veins,  and  on  the  root, 


208  Diseases  of  Truck  Crops 

by  a  blackening  and  decaying  of  the  stem;  see 
also  p.  190.  Kale  is  also  attacked  by  club  root  Plas- 
modiophora  brassica  Wor.,  see  p.  1 86. 

DISEASES  OF  THE  MUSTARD  (Brassica 
Japonicd) 

Garden  mustard  Brassica  Japonica  is  cultivated 
for  its  foliage.  It  is  used  as  a  green,  relished  for  its 
edible  qualities,  and  as  a  spring  tonic.  Mustard  is 
subject  to  the  following  diseases: 

BLACK  ROT,  see  CABBAGE,  p.  190. 

CLUB  ROOT,  see  CABBAGE,  p.  186. 

WHITE  RUST  (fig.  35  b-e),  see  RADISH,  p.  193. 

DISEASES  OF  THE  RADISH  (Raphanus  sativus) 

Radish  is  subject  to  many  diseases  in  common  with 
the  cabbage  and  numerous  other  crucifers. 

CLUB  ROOT,  see  CABBAGE,  p.  186. 

BLACK  ROT 
Caused  by  Pseudomonascampestris  (Pam.)  Ew.  Sm. 

Black  rot  on  radish  is  confined  mostly  to  the  tender 
white-rooted  varieties,  especially  the  Icicle.  The 
black-rot  germ  penetrates  the  lateral  feeding  rootlets, 
from  which  it  works  its  way  in  the  main  root.  In 
cutting  across  a  diseased  radish,  its  interior  fibro- 
vasculaf  bundles  are  found  to  be  blackened.  Such 


Family  Cruciferae  209 

radishes  are  useless  for  the  market.  The  disease 
seldom  attacks  the  red  or  the  black-skinned  varieties. 
For  further  consideration  of  black  rot  see  p.  190. 

SCAB 
Caused  by  Actinomyces  chromogenus  Gasp. 

Scab  is  not  a  common  field  disease  of  radishes.  It 
is,  however,  found  to  be  troublesome  on  the  crop 
grown  in  greenhouses.  The  French  Breakfast  is 
commonly  susceptible  to  the  disease.  The  trouble 
may  be  expected  if  the  crop  is  planted  in  a  soil  which 
previously  produced  a  potato  crop  that  was  badly 
scabbed  or  where  infected  manure  was  used,  or  too 
much  lime  applied.  For  further  description  of  scab, 
seep.  317. 

DAMPING  OFF 
Caused  by  Rheosporangium  aphanidermatum  Ed. 

This  disease,  which  was  studied  and  described  by 
Edson,1  is  very  troublesome,  attacking  radish  and 
beet  seedlings  alike. 

Symptoms.  The  disease  is  confined  to  the  root 
system,  seldom  appearing  above  ground.  Diseased 
plants  have  a  flabby  appearance,  and  the  normal  green 
of  the  foliage  is  displaced  by  a  slightly  yellowish  tinge. 

1  Edson,  H.  A.,  U.  S.  Dept.  of  Agr.,  Jour.  Agr.  Research,  4:  279- 
292, 


210  Diseases  of  Truck  Crops 

In  severe  cases  the  entire  stand  may  be  wiped  out. 
On  carefully  pulling  out  a  diseased  plant,  we  shall 
find  the  side  rootlets  blackened,  shriveled,  and  dead 
(fig.  35  a).  Frequently  the  plant  attempts  to  pro- 
duce new  roots  above  the  diseased  area.  In  this 
case,  however,  there  is  only  partial  recovery.  The 
disease  is  most  prevalent  in  the  heavy  soils. 

The  Organism.  In  general  characters,  the  organ- 
ism may  be  mistaken  for  Pythium  de  Baryanum,  but 
it  differs  from  the  latter  in  its  asexual  fruiting  bodies. 
The  mycelium  of  Rheosporangium  aphanidermatum 
is  hyaline,  non -septate  (fig.  35  c),  and  grows  profusely 
on  solid-  media.  Mycelium  of  cultures  one  or  two 
days  old  exhibits  considerable  streaming  of  proto- 
plasm which  seems  always  directed  toward  the  tip 
end  of  the  hyphae.  This  protoplasmic  streaming 
results  in  the  final  accumulation  in  protoplasmic 
material,  and  in  consequence  of  a  considerable  en- 
largement of  the  tip  of  the  thread.  Finally  a  cell 
wall  is  laid  down  which  cuts  off  the  swollen  portion 
from  the  rest  of  the  mycelium.  This  swollen  body 
which  Edson  named  presoporangium  (fig.  35  b)  has 
the  appearance  of  a  zoosporangium  but  in  reality 
it  differs  from  it  since  it  gives  rise  not  to  zoospores, 
as  might  be  expected,  but  to  an  independent  body 
which  later  gives  rise  to  zoospores.  The  pre- 
soporangium now  absorbs  water  and  its  outer  wall 
ruptures,  from  which  is  seen  to  flow  out  a  mass  of 
protoplasm  enclosed  in  a  thin  cell  wall.  This  es- 
caped mass  is  really  the  young  zoosporangium,  the 
cytoplasm  of  which  finally  cleaves  into  zoospores. 


FIG.  35.     RADISH  DISEASES. 

a.  Young  radishes  attacked  by  Rheosporangium  damping  off,  b.  presporangium 
C.  mycelium  of  Rheosporangium  aphanidermatum ,  d.  fertilization  of  the  female 
oogonium  by  the  male  antheridium,  e.  mature  oospore,  /.  root  knot  (b  to  e  afler 
Edson). 


Family  Cruciferae  211 

With  the  maturity  of  the  sporangium  its  cell  wall 
dissolves,  liberating  the  swarm  spores  which  swim 
about  for  a  time,  then  come  to  rest,  round  up,  and 
increase  in  size  and  germinate  by  sending  out  a  germ 
tube.  Oospores  are  produced  in  a  fashion  somewhat 
similar  to  Pythium.  The  oogonia  are  formed  as 
terminal  spherical  bodies.  The  antheridium  de- 
velops terminally,  lying  close  to  the  oogonium. 
The  content  of  the  antheridium  is  emptied  into  the 
body  of  the  oogonium  (fig.  35  d)  and  fertilization  is 
effected.  The  mature  oospore  (fig.  35  e)  is  spherical 
with  a  thick  smooth  or  undulated  wall  and  germin- 
ates by  means  of  a  germ  tube. 

Control.  When  the  disease  is  present  on  a  large 
scale,  it  is  useless  to  attempt  to  control  it.  The 
fungus,  as  we  have  seen,  is  a  soil  parasite,  hence  soil 
treatments  discussed  on  p.  53  could  not  be  consid- 
ered on  a  large  scale.  As  far  as  we  know,  this  disease 
attacks  only  radish  and  beet  seedlings.  Badly  in- 
fected fields  should  be  devoted  to  other  crops  for 
several  years  until  the  parasite  is  starved  out.  On 
a  small  scale,  infected  soils  may  be  treated  with 
formaldehyde  (see  p.  53),  or  fire  (see  p.  56). 
DOWNY  MILDEW,  see  CABBAGE,  p.  194. 

WHITE  RUST 
Caused  by  Cystopus  candidus  (Pers.)  Lev. 

The  damage  caused  by  white  rust  depends  largely 
on  seasonal  conditions.     The  disease  is  most  preva- 


212  Diseases  of  Truck  Crops 

lent  on  early  spring  or  fall  radish.  The  greatest 
damage  done  by  this  trouble  is  to  the  seed  crop. 

Symptoms.  On  the  leaves,  white  rust  is  manifested 
as  white  raised  pimples  or  sori  (fig.  33  b)  character- 
istic of  all  white  rusts.  When  the  surface  of  the 
sori  breaks  open  a  white  powder,  which  consists  of  the 
spores  of  the  fungus,  is  liberated.  On  the  flower 
organs  of  the  radish,  the  symptoms  of  the  disease  are 
especially  striking.  The  ovary  sacs,  the  stamens, 
corolla,  and  calyx  become  hypertrophied  and  dis- 
tended, resembling  abnormal  leaves. 

It  has  been  questioned  whether  the  white  rust  of 
the  radish  is  the  same  as  that  which  attacks  other 
crucifers  such  as  cabbage,  mustard,  etc.  While 
much  remains  to  be  learned,  the  investigations  of 
Melhus  throw  much  light  on  the  subject.  Melhus1 
had  no  trouble  in  infecting  the  rat- tail  radish  (Raph- 
anus  caudatus)  with  conidia  taken  from  ordinary  radish 
(Raphanus  sativus).  Melhus  also  secured  infection 
by  sowing  conidia  from  the  radish  on  white  mustard 
(Brassica  alba)  and  cabbage  (Brassica  oleracea).  At 
no  time,  however,  was  it  possible  to  infect  more 
than  fifty  per  cent,  of  the  cotyledons  or  leaves  of  the 
white  mustard  which  were  inoculated.  With  the 
cabbage  it  was  still  more  difficult  to  secure  infection. 
Of  the  fifteen  varieties  inoculated  less  than  one  per 
cent,  of  the  plants  became  infected. 

No  infection  could  be  obtained  when  sowing  spores 
of  Cystopus  candidus  from  radish  on  ten  varieties  of 

1  Melhus,  T.  E.,  Wisconsin  Agr.  Expt.  Sta.  Research  Bui.,  15: 25- 
83,1911. 


Pamily  Cruciferae  213 

turnips  (Brassica  rapa),  black  mustard  (Brassica 
nigrd),  rutabaga  (Brassica  campestris),  shepherd's 
purse  (Capsella  bursa-pastoris) ,  garden  cress  (Le- 
pidium  sativum),  wild  pepper  grass  (Lepidiumvirgini- 
cum),  hedge  mustard  (Sisymbrium  officinale  and  S. 
altissimum),  candy- tuft  (Iberis  umbellata),  water  cress 
(Nasturtium  officinale),  and  wall  flower  (Cheiranihus 
cheiri).  From  the  above  experiments,  it  would  seem 
that  in  dealing  with  the  white  rust  fungus,  Cystopus 
candidus,  it  is  possible  that  there  exist  distinct  races 
or  strains,  all  of  which  are  specialized  to  certain 
special  hosts  of  the  various  crucifers.  The  best 
infection  is  secured  when  the  seedlings  of  the  host 
plant  are  chilled.  This  is  why  white  rust  is  more 
prevalent  in  cool  seasons. 

The  Organism.  Cystopus  candidus  has  two  fruit- 
ing stages.  The  summer  or  conidial  stage  is  made  up 
of  simple  chains  of  spores  (fig.  33  c).  The  latter  are 
separated  one  from  the  other  by  a  minute  beak-like 
projection.  Each  spore  or  zoosporangium  germi- 
nates by  six  or  more  swarm  spores,  or  zoospores. 
These,  when  set  free,  swim  around,  then  come  to  rest 
and  germinate  by  means  of  a  germ  tube.  The 
oospore  or  sexual  spore  of  the  Cystopus  is  formed 
later  in  the  season.  The  oogonia  and  antheridia  (fig. 
33  d)  are  developed  within  the  infected  host  tissue. 
Fertilization  proceeds  in  the  same  way  as  in  Pythium. 
The  mature  oospore  has  a  thick,  sculptured  wall,  and 
is  brown  in  color.  The  oospores  germinate  in  the 
same  way  as  the  zoosporangium,  i.  e.,  by  the  forma- 
tion of  zoospores  (fig.  33  e). 


214  Diseases  of  Truck  Crops 

Control.     Burning  of  all  infected  trash  and  crop 
rotation  are  the  best  effective  remedies. 
ROOT  ROT,  see  BEET  p.  122,  128. 
ROOT  KNOT  (fig.  35  f),  see  BEET  p.  129. 

DISEASES  OF  THE  TURNIP  (Brassica  Rapa) 

CLUB  ROOT,  see  CABBAGE,  p.  186. 

BLA^K  ROT 

Caused  by  Pseudomonas  campestris  (Pam.)  Ew.  Sm. 

Black  rot  in  turnips  is  apparently  confined  to  the 
roots.  Infected  plants  may  live  a  long  time,  and 
show  no  symptoms  on  the  leaves.  The  roots  of 
such  plants,  however,  are  stunted,  abnormal  in  shape, 
and  very  narrow.  The  interior  tissue  is  dry  rotted 
and  blackened,  emitting  a  characteristic  strong  odor. 
For  further  description  of  the  black  rot,  see  p.  317. 

SCAB,  see  BEET,  p.  120,  and  POTATO  p.  317. 

WHITE  RUST,  see  RADISH,  p.  211. 

DOWNY  MILDEW,  see  CABBAGE  p.  194. 

DROP  (fig.  36  g),  see  CABBAGE,  p.  194. 

ANTHRACNOSE 

Caused  by  Colletotrichum  Higginsianum  Sacc. 

Anthracnose  is  a  new  disease  which  has  recently 
been  studied  and  described  by  Higgins1  in  Georgia. 

1  Higgins,  B.  B.,  U.  S.  Dept.  of  Agr.,  Jour,  of  Agr.  Research,  10: 
157-161,  1917. 


FIG.  36.     TURNIP  DISEASES. 

a.  and  b.  Anthracnose,  c.  cross  section  through  acervulus,  d.  anthracnose  spores 
e.  Cylindrosporium  leaf  spot,  /.  Phoma  rot,  g.  Sclerotinia  rot  (c.  and  d  pfter 
Higgins). 


Family  Cruciferae  215 

The  disease  attacks  the  leaves  (fig.  36  a-b),  causing 
small  circular  gray  or  straw-colored  spots.  The 
acervuli  and  the  salmon-pink  spore  clusters  appear 
only  under  moist  conditions.  The  causative  fungus 
differs  from  Colletotrichum  brassiccz  Sch.  and  Sacc. 
The  acervuli  are  small,  scattered  on  both  surfaces 
of  the  spots.  The  conidiophores  are  short  (fig.  36  c), 
conidia  hyaline  cylindrical  one  celled  (fig.  36  d),  setae 
dark  brown  to  black,  slender,  I  to  3  septate  (fig.  36  c). 
On  the  stems  the  spots  are  more  elongated.  On 
the  leaves  the  spots  are  said  to  be  much  smaller 
than  those  produced  by  Cylindrosporium  bmssictz 
F.  and  R.  (fig.  36  e).  Anthracnose  is  not  carried 
with  the  seed.  No  method  of  control  is  as  yet 
known. 

PHOMA  ROT 
Caused  by  Phoma  napobrassiccs  Rost. 

Phoma  rot  is  a  disease  which  is  common  in  the 
north  of  England.  It  is  also  found  in  New  Zealand 
and  in  Canada.  In  the  United  States  it  has  been 
reported  but  once,  by  Clinton1  of  Connecticut. 

Phoma  rot  seems  to  be  a  storage  trouble,  although 
the  disease  is  first  introduced  from  the  field. 

Symptoms.  In  the  field,  the  disease  is  first  noticed 
at  digging  as  a  rot  around  the  crown,  the  top  of  the 
plant  readily  pulling  off.  In  storage  the  disease  is 

Clinton,  G.  P.,  Connecticut  Agr.  Expt.  Sta.,  36th.  Ann.Rept.  : 
355-353,  1912. 


216  Diseases  of  Truck  Crops 

manifested  on  the  roots  as  a  dry  rot  which  appears 
first  as  scattered  sunken  spots  bordered  by  dark  areas 
(fig.  36  f).  The  pycnidia  of  the  fungus  are  generally 
absent  from  the  spots,  but  they  appear  in  great 
abundance  when  the  roots  are  placed  under  favor- 
able conditions  of  moisture. 

Control.  It  is  doubtful  if  Phoma  rot  can  be  con- 
trolled by  spraying  the  foliage  in  the  field.  Since 
the  disease  is  carried  over  in  the  roots,  it  would  be 
dangerous  to  feed  them  to  stock  or  dump  them  on  the 
manure  pile.  Rotation  should  be  practiced  where 
the  disease  has  appeared  more  than  once  in  the  same 
field.  Care  should  be  taken  that  no  diseased  roots 
be  permitted  to  enter  the  storage  house  or  cellar. 
The  roots  should  be  thoroughly  dried  before  storing, 
and  the  house  or  cellar  should  be  kept  moder- 
ately cool  and  ventilation  resorted  to  wherever 
possible. 

POWDERY  MILDEW 
Caused  by  Erysiphe  polygoni  D.  C. 

Powdery  mildew  has  not  been  known  to  cause 
any  considerable  damage  to  turnips  in  the  United 
States.  It  is  characterized  by  the  presence  of 
powdery  white  patches  on  both  surfaces  of  the  leaf. 
Besides  affecting  the  turnip,  Erysiphe  polygoni  has 
been  recorded  on  about  three  hundred  different  hosts, 
especially  the  garden  pea.  For  methods  of  control, 
see  p.  367. 


FIG.  37.    TURNIP  DISEASE. 


a.  Macrosporium  leaf  spot,  b.  Macrosporium  herculeum,  showing 
conidiophores  and  conidia,  c.  individual  conidium  of  M .  herculeum 
(a.  to  c.  after  F.  C.  Stewart). 


Family  Crucifcrae  217 

MACROSPORIUM  LEAF  SPOT 
Caused  by  Macrosporium  herculeum  E.  and  M. 

Leaf  spot  often  attacks  the  flat  turnip  and  horse- 
radish. On  turnips  it  is  manifested  as  brittle  circular 
spots  on  the  leaf  (fig.  37  a).  When  numerous,  the 
spots  usually  fall  out,  giving  a  shot-hole  appearance. 
The  long  club-shaped  spores  (fig.  37  c)  of  the  fungus 
are  borne  on  long  conidiophores  (fig.  37  b)  on  the 
exterior  of  the  dead  tissue.  Should  treatment  seem 
advisable,  spraying  with  Bordeaux  mixture  is  re- 
commended. 

WEEDS 

Of  the  many  cruciferous  weeds  which  truckers  have 
to  contend  with,  the  following  few  may  be  mentioned : 
Winter  cress  (Barbarea  vulgaris),  shepherd's  purse 
(Capsella  bursa-pastoris),  cow  cress  (Lepidium  cam- 
pestre),  pepper  grass  (Lepidium  virginicum).  The 
above  mentioned  weeds  and  many  other  crucifers 
are  subject  to  club  root,  black  rot,  white  rust,  and 
downy  mildew. 

It  is  evident  therefore  that  clean  culture  is  impor- 
tant. These  weeds  must  not  be  tolerated  if  we  are 
completely  to  eradicate  the  diseases  of  the  cultivated 
crucifers. 


CHAPTER  XIV 

FAMILY  CUCURBITACE^E 

THE  Cucurbit  family  contains  numerous  valuable 
truck  crops.  Those  grown  for  their  economic  value 
may  be  mentioned:  cantaloupe,  cucumber,  pumpkin, 
squash,  and  watermelon.  According  to  the  Thir- 
teenth Census  of  the  United  States,  the  total  area 
devoted  to  cantaloupes  and  muskmelons  in  America 
was  52,419  acres,  and  the  total  crop  valued  at 
$3,604,636.  The  States,  ranked  according  to  the 
acreage  devoted  to  these  crops,  were  California, 
New  Mexico,  New  Jersey,  Indiana,  Maryland, 
Florida,  Georgia,  Illinois,  North  Carolina,  Michigan, 
Colorado,  Missouri,  Texas,  Ohio,  Tennessee,  and 
Delaware.  States  with  less  than  one  thousand  acres 
are  omitted. 

The  total  area  in  the  United  States  in  1909  given 
up  to  cucumbers  was  estimated  at  32,310  acres, 
and  the  total  crop  valued  at  $2,719,340.  The  States 
ranked  according  to  the  area  devoted  to  cucumbers 
were  Michigan,  New  York,  Illinois,  Indiana,  Florida, 
Virginia,  New  Jersey,  Wisconsin,  Texas,  and  Min- 
nesota. States  with  less  than  one  thousand  acres 

are  omitted. 

218 


Family  Cucurbitaceae  219 

The  total  area  devoted  to  watermelons  in  the 
United  States  in  1909  was  estimated  at  137,005  acres, 
and  the  total  crop  valued  at  $4,453,101.  The  States 
which  lead  in  rank  according  to  acreage  devoted  to 
watermelon  were :  Texas,  Florida,  Georgia,  Missouri, 
Indiana,  Illinois,  California,  Oklahoma,  North  Caro- 
lina, South  Carolina,  Alabama,  Iowa,  Arkansas, 
Kansas,  Virginia,  Tennessee,  Maryland,  New  Jersey, 
Mississippi,  Kentucky,  and  Louisiana. 

DISEASES  OF  THE  CANTALOUPE 
(Cucumis  melo) 

The  cantaloupe  is  subject  to  numerous  diseases 
which  often  reduce  the  yield  of  the  crop  and  en- 
tail heavy  money  losses.  Fortunately  most  of  the 
diseases  may  be  controlled. 

BACTERIAL  WILT 
Caused  by  Bacillus  tracheiphilus  Ew.  Sm. 

Bacterial  wilt  may  be  regarded  as  one  of  the  most 
serious  diseases  of  the  cantaloupe.  It  has  a  very  wide 
distribution,  but  it  is  said  to  be  restricted  in  its 
Southern  distribution.  The  same  disease  also  at- 
tacks the  cucumber,  pumpkin,  and  squashes.  The 
trouble  is  not  known  to  occur  on  hosts  outside  of  the 
Cucurbitaceae.  Even  in  this  family  there  are  plants 
which  are  not  subject  to  its  attack.  Dr.  Erwin 
Smith  succeeded  in  artificially  inoculating  the  fol- 
lowing cucurbits :  Cucumis  odoratissimus,  C.  anguria, 


220  Diseases  of  Truck  Crops 

Benincasa   cerifera,  Cucurbita  fcetidissima,  C.  call- 
fornica,  Echinocystis  lobata. 

Symptoms.  The  symptoms  of  bacterial  wilt  are 
very  striking.  At  first  a  few  leaves  of  the  plant  are 
wilted.  Soon  after  the  entire  plant  wilts  and  dies. 
In  cutting  through  an  infected  stem,  a  whitish  viscid 
exudate  oozes  out  from  the  vascular  bundles  of  the 
cut  surface.  In  placing  one  finger  on  the  viscid 
substance  and  then  gently  removing  it,  the  bac- 
teria will  be  strung  out  into  numerous  delicate 
threads  resembling  cobwebs.  The  disease  works 
quickly  and  the  change  of  leaf  color  from  bright 
to  ^dull  green  is  also"  sudden.  Cantaloupes,  unlike 
squash,  show  no  tendency  to  recover  temporarily 
from  wilt. 

Bacterial  wilt  is  spread  about  through  the  bites  of 
leaf -eating  beetles,  such  as  striped  cucumber  beetle, 
(Diabrotica  vittatd). 

The  Organism.  B.  tracheiphilus  is  a  short  straight 
rod  with  rounded  ends.  The  organism  occurs  singly 
in  pairs  and  rarely  in  chains  of  four;  it  is  motile  by 
means  of  flagella.  It  grows  slowly  on  gelatine  which 
is  not  liquefied.  On  potato  cylinders  growth  is  vigor- 
ous, resulting  in  a  gray-white  film  with  no  changes 
manifested  in  the  substratum.  There  is  no  gas  pro- 
duction and  the  organism  is  aeorobic. 

Control.  Infection  begins  at  a  place  of  injury 
produced  by  the  bite  or  puncture  of  insects.  Hence 
any  attempt  at  controlling  wilt  should  first  aim 
at  controlling  insect  pests.  For  further  control, 
see  p.  232. 


FIG.  38.    CANTALOUP  DISEASES. 

a.  Soft  rot,  b.  individual  germs  of  soft  rot  (a.  and  b.  after  Giddings),  c.  young 
cantaloup  plant  artificially  inoculated  with  Mycosphaerella  wilt,  d.  section  through 
a  perithecium  of  Mycospharella  citrullina,  showing  immature  asci,  e.  ascospores  of 
M.  citrullina  (c.  to  e.  after  Grossenbacher),/.  Alternaria  leaf  blight,  g.  Conidiophores 
and  spore  of  Macros porium  cucumerinum  (after  Chester),  h.  Southern  blight. 


Family  Cucurbitaceae  221 

SOFT  ROT 
Caused  by  Bacillus  melonis  Gid. 

Soft  rot  is  a  disease  which  attacks  the  melon  fruit 
only.  The  losses  from  this  trouble  often  run  as  high 
as  twenty-five  per  cent,  of  the  crop.  It  is  prevalent 
in  seasons  with  prolonged  dry  weather  followed  by  a 
wet  spell.  This  results  in  the  uneven  growth  and 
development  of  the  fruit  and  hence  in  various  crack- 
ings in  its  surface.  Infection  follows  the  place  of 
injury,  especially  when  the  crack  (fig.  38  a)  occurs 
at  a  place  where  the  cantaloupe  touches  the  ground. 
The  rot  produced  is  soft  with  an  offensive  odor. 

The  Organism.  Bacillus  melonis  is  a  short  rod 
(fig.  38  a)  with  rounded  ends,  occurring  singly  or  in 
short  chains  of  two  to  three,  and  motile  by  means  of 
flagella.  It  forms  no  endospores,  no  capsule,  and  no 
involution  forms.  It  completely  liquefies  gelatine 
in  fourteen  days.  No  gas  is  formed,  and  no  very  dis- 
tinct odor  is  noticed.  It  dies  by  drying  and  exposure 
to  light. 

Control.  Wherever  possible,  irrigation  should  be 
resorted  to'in  dry  weather.  This  will  encourage 
even  growth  and  prevent  cracking  of  the  fruit.  In 
wet  weather  spraying  with  Bordeaux  mixture  is  re- 
commended. Occasional  turning  of  the  melons  to 
expose  them  to  light  on  all  sides  will  also  help.  Dis- 
eased refuse  should  be  destroyed  and  not  be  fed  to 
stock. 

DOWNY  MILDEW,  see  CUCUMBER,  p.  230. 


222  Diseases  of  Truck  Crops 

POWDERY  MILDEW 
Caused  by  Erysiphe  polygoni  D.  C. 

This  disease  is  the  same  as  the  mildew  which  at- 
tacks garden  peas,  cucumbers,  and  numerous  other 
hosts.  Mildew  is  more  prevalent  on  greenhouse 
melons  and  cucumbers  than  on  those  grown  outdoors. 
It  is  characterized  by  powdery  white  patches  on  the 
leaves.  The  trouble  is  seldom  serious  enough  in  the 
field  to  warrant  treatment. 

MYCOSPILERELLA  WILT 
Caused  by  Mycosph&rella  citrulina  (Sm.)  Gr. 

Although  this  form  of  wilt  is  often  a  greenhouse 
trouble,  it  is  nevertheless  a  serious  disease  on  out- 
door cantaloupes  and  watermelons.  Grossenbacher1 
found  that  infection  is  localized  at  the  nodes  and  not 
at  the  internodes  (fig.  38  c).  The  injury  from  Red 
Spider  or  other  sucking  insects  is  perhaps  responsible 
for  opening  the  way  to  this  disease.  A  character- 
istic of  the  trouble  is  that  the  edges  of  the  infected 
areas  are  oily  green  to  raisin-colored  gum.  The 
older  parts  of  the  spots  are  either  dark  and  gummy 
or  gray  and  dry,  bearing  numerous  brown  pycnidia. 

The  Organism.  The  perithecia  (fig.  38  d)  are 
globular  to  inverted  top-shaped,  rough,  dark  brown 

1  Grossenbacher,  J.  G.,    New   York    (Geneva)    Agr.  Expt.  Sta. 
Tech.  Bui.  9  :  197-229,  1909. 


Family  Cucurbitaceae  223 

to  black,  erumpent,  and  finally  almost  superficial. 
The  necks  of  the  perithecia  are  papillate.  The 
ascospores  are  cylindrical,  two-celled,  hyaline,  and 
slightly  constricted  at  the  septum  (fig.  38  e). 

Control.  Spraying  with  Bordeaux  mixtures  when 
the  plants  are  about  half  grown  and  before  the  disease 
appears  is  recommended.  Spraying  should  be  con- 
tinued so  that  the  growing  parts  are  kept  covered 
with  the  fungicide. 

ANTHRACNOSE,  see  WATERMELON,  p.  240. 

LEAF  BLIGHT 
Caused  by  Alternaria  brassica  var.  nigrescens  Pegl. 

Leaf  blight  is  a  very  destructive  disease,  often 
ruining  entire  patches  which  otherwise  looked  very 
promising.  In  some  seasons,  it  is  the  greatest  draw- 
back to  successful  melon  culture. 

Symptoms.  The  disease  begins  as  small  round 
spots  which  gradually  enlarge.  These  spots  are  dry, 
brown  in  color  and  made  up  of  concentric  rings  or 
zones  (fig.  38  f  and  g).  Usually  the  spots  are  very 
numerous  and  their  presence  causes  the  leaves  to  curl 
and  dry  up  prematurely,  leaving  bare  vines  and  un- 
protected fruit.  As  a  result,  the  melons  ripen  early 
and  have  an  insipid  taste,  and  are  very  poor  shippers. 
Leaf  blight  is  most  serious  in  fields  where  canta- 
loupes are  grown  too  long  on  the  same  field. 

Blight  Resistant  Cantaloupes.  In  selecting  for 
blight  resistant  cantaloupe  (fig.  39  a-  b),  we  must  con- 


224     Diseases  of  Truck  Crops 

sider  (i),  the  yielding  quality  of  the  strain;  (2),  the 
earliness  in  maturing;  (3),  resistant  qualities;  (4), 
form,  size,  and  netting;  (5),  texture  and  edible  quali- 
ties; (6),  shipping  qualities.  Blinn x  found  that  resis- 
tance in  cantaloupes  seems  to  go  hand  in  hand  with 
the  netting  of  the  rind.  Good  netting  seems  also  to 
favor  good  shipping  melons  with  fine  flavor.  It 
seems  that  the  closer  the  netting  the  better  will  the 
fruit  be  protected  from  loss  of  weight  from  evapora- 
tion. The  Rocky  Ford  Pollock  strain  is  claimed  to  be 
resistant  to  blight.  Control  by  spraying,  see  cu- 
cumber, p.  232. 

PHYLLOSTICTA  LEAF  SPOT 
Caused  by  Phyllosticta  cucurbitacearum  Sacc. 

This  disease  has  not  proved  as  serious  as  leaf 
blight.  It  is  characterized  by  spots  which  are  light 
in  color.  The  pycnidia  are  pointed,  the  spores 
oblong  and  curved,  hyaline  and  one-celled.  The  dis- 
ease may  be  controlled  by  spraying,  see  p.  232. 

CERCOSPORA  LEAF  SPOT 
Caused  by  Cercospora  cucurbits  E.  and  E. 

This  disease  behaves  very  much  like  leaf  blight. 
In  the  former,  however,  the  spots  are  usually  of  a 
1  Blinn,  P.  K.,  Colorado  Agr.  Expt.  Sta.  Bui.  104:  3-15, 1905. 


Family  Cucurbitaceae  225 

lighter  color,  and  are  more  angular  in  form,  being 
limited  by  the  veins  of  the  leaf.  The  methods  of 
control  are  the  same  as  for  leaf  blight,  see  p.  223. 

SOUTHERN  BLIGHT 

* 
Caused  by  Sclerotium  Rolfsii  Sacc. 

Southern  blight,  a  disease  that  attacks  a  large 
variety  of  hosts,  is  a  serious  cantaloupe  disease  in  the 
Southern  States.  The  injury  in  most  cases  is  con- 
fined to  the  foot  of  the  stem,  resulting  in  its  girdling 
and  rotting  and  the  final  dying  of  the  affected  plant. 
With  the  cantaloupe,  the  disease  attacks  the  fruit, 
infection  usually  taking  place  at  a  point  where  it 
touches  the  ground  (fig.  38  h).  The  disease  appears 
first  as  a  slight  soft  spot  which  enlarges  quickly, 
changing  the  entire  mass  of  the  fruit  to  a  mushy  pulp. 
The  exterior  of  the  affected  melon  is  seen  to  be  cov- 
ered with  a  white  cottony  growth  consisting  of  the 
mycelium  of  the  fungus.  Later  there  appear  numer- 
ous whitish  bodies  known  as  sclerotia  which  turn 
yellowish  and  then  brown.  They  help  to  carry  the 
fungus  over  the  winter.  For  methods  of  control,  see 
tomato,  p.  353. 

ROOT  KNOT,  see  NEMATODE,  p.  49. 

CARE  IN  THE  SHIPPING  OF  CANTALOUPES 

As  a  rule,  the  greatest  per  cent,  of  the  cantaloupe 
crop  is  shipped  to  distant  markets.     Growers  often 
is 


226  Diseases  of  Truck  Crops 

lose  heavily  from  rotting  of  the  fruit  before  it  reaches 
its  destination.  Most  of  the  loss  may  be  reduced  to 
a  minimum  or  entirely  prevented,  provided  growers 
are  willing  to  devote  more  attention  to  certain 
fundamental  considerations  suggested  by  More  and 
Branch.1 

a.  Need  of  Quality.     No  one  can  deny  the  fact 
that  products  which  are  poorly  grown,  poorly  har- 
vested, and  poorly  packed  and  shipped,  are  a  direct 
loss  to  the  grower  and  a  serious  drawback  to  the 
market.     The  consumer  to-day  insists  on  quality, 
and  the  grower  who  is  to  succeed  cannot  ignore  this 
demand.     Cantaloupes  to-day  are  grown  more  ex- 
tensively than  formerly.     Competition  therefore  is 
more  keen,  and  growers  in  the  West  are  more  handi- 
capped, because  their  products  must  travel  longer 
distances,  and  therefore  require  more  care  in  handling. 
By  selecting  fruit  which  matures  early  and  at  the 
same    time    possesses    better    edible    and    shipping 
qualities  the  difficulty  will  be  at  least  partly  solved. 

b.  Care  in  Picking  and  Handling.     Success   in 
shipping  depends  largely  on  proper  picking  and  hand- 
ling.   With  the  "Netted  Gem"  or  "Green  Nets," 
the  melons  should  not  be  harvested  until  completely 
netted.     The   netting    should   be   well   raised   and 
rounded  out  on  the  surface.     With  immature  melons 
the  netting  is  flat  and  creased  on  top.     For  shipping 
short  distances  the  melons  may  be  picked  "full  slip, " 
i.  e.  just  as  soon  as  the  stem  separates  cleanly  from 

1  More,  C.  T.,  and  Branch,  G.  V.,  U.  S.  Dept.  of  Agr.  Farm.  Bui. 
707  : 1-23,  1916. 


Family  Cucurbitacese  227 

the  melon,  leaving  a  cuplike  cavity  and  tearing  with 
it  none  of  the  rind.  When  shipping  long  distances 
the  melons  are  picked  on  "half  slip,"  in  which  case 
only  part  of  the  stem  pulls  away  from  the  fruit,  the 
rest  breaking.  It  is  essential  that  the  fruit  be 
handled  carefully  in  the  field,  avoiding  bruises  and 
cuts.  At  the  packing  shed,  the  same  care  should  be 
observed. 

c.  Care  in  Packing.     Good  shipping  also  depends 
on  careful  packing.     Only  standard  containers  for 
shipping  should  be  used.     The  crate  has  become  the 
standard    container    for    shipping    melons.     Crates 
should  be  made  of  clean,  smooth,  strong  lumber,  with 
all  knotty  and  cross-grained  slats  discarded.     Dirty 
and  second-hand  crates  should  not  be  used.     Crates 
used  in  the  field  in  harvesting  should  not  be  used 
for  shipping. 

d.  Need  of  Grading.    Up-to-date  growers  take  pains 
to   grade   their   product  carefully   before   packing. 
A  careful  grading  excludes  melons  which  are  poorly 
netted,  also  known  as  "slickers."     It  is  also  essen- 
tial to  exclude  melons  which  are  cracked,  bruised, 
diseased,  ill-shaped,  over  ripe,  as  well  as  those  that 
are  immature  and  those  with  soft  stems.     In  pack- 
ing, melons  of  the  same  size  and  grade  only  should 
be  put  in  the  same  container. 

e.  Care  in  Handling.     In  hauling  melons  from  the 
packing  sheds  to  the  car,  only  wagons  with  good 
springs  should  be  used.     Hauling  wagons  should  also 
be  provided  with  tarpaulin  covers  to  protect  the  fruit 
from  the  sun,  rain,  or  dust.     The  crates  should  be 


228  Diseases  of  Truck  Crops 

carefully  unloaded  into  cars  which  are  iced,  if  the 
melons  are  to  be  shipped  long  distances.  When  the 
cars  have  been  properly  filled,  they  should  be  dis- 
patched as  early  as  possible.  Freight  agents  should 
see  that  cars  are  not  delayed  on  the  road. 

DISEASES  OF  THE  CUCUMBER  (Cucumis 
sativus) 

Cucumbers,  like  cantaloupes,  are  subject  to  vari- 
ous diseases  which  render  them  unfit  for  the  market 
or  for  pickling. 

MOSAIC  OR   "WHITE"  OR   "LITTLE  PICKLE" 
Cause  unknown. 

Mosaic  has  been  found  in  Wisconsin,  Michigan, 
Indiana,  Ohio,  Iowa,  Illinois,  Vermont,  New  York, 
Louisiana,  New  Jersey,  Minnesota,  Massachusetts, 
and  Virginia. 

Symptoms.  The  first  sign  appears  as  a  yellow 
mottling  near  the  stem  end  of  the  fruit.  Later  the 
light  areas  are  found  all  over  the  cucumber,  and  the 
darker  portions  frequently  form  protuberances. 
Some  fruits  retain  their  green  color  and  show  the  dis- 
ease only  by  being  distorted.  The  leaves  too  be- 
come mottled,  light  to  dark  green  (fig.  40  a),  and 
sometimes  wrinkled;  the  stems  and  petioles  too  are 
dwarfed  and  distorted.  Affected  leaves  die  prema- 
turely and  are  replaced  by  others,  which  in  turn  con- 


FIG.  39.     RESISTANT  CANTALOUP  STRAIN. 

a.  Cantaloup  hill,  destroyed  by  Alternaria  leaf  blight,  b.  cantaloup  hill  resistant 
to  Alternaria  blight,  a.  and  b.  same  variety  (Rockyford)  growing  in  same  field 
under  equal  conditions. 


Family  Cucurbitaceae  229 

tract  the  disease.  The  trouble  is  spread  by  insects, 
the  principal  of  which  is  the  melon  louse,  Aphis 
gossypii  Glov.,  as  well  as  the  striped  cucumber  beetle, 
Didbrotica  vittala.  Satisfactory  control  methods  are 
still  wanting.  Diseased  plants  should  be  destroyed 
and  the  field  sprayed  for  insect  pests. 

BACTERIAL  WILT 
Caused  by  Bacillus  tracheiphillus  Ew.  Sm. 

The  symptoms  and  damage  caused  by  this  wilt 
have  already  been  discussed  under  the  cantaloupe, 
p.  219.  Recent  investigations  by  Rand  and  Enlows1 
have  shown  that  seeds  from  diseased  plants~fail  to 
reproduce  wilt.  This  is  true  not  only  for  the  cucum- 
ber, but  also  for  all  the  other  cucurbit  hosts  which  are 
subject  to  this  trouble.  Of  the  numerous  varieties 
of  cucumber  and  cantaloupe  tested,  none  shows 
promise  of  resistance.  While  the  Marblehead,  Gol- 
den Bronze,  and  Boston  Marrow  are  very  susceptible 
varieties  of  the  squash,  the  Mammoth  White  Bush 
and  the  Early  White  Bush  seem  to  be  immune  to  wilt. 

ANGULAR  LEAF  SPOT 
Caused  by  Pseudomonas  lachrymans  Sm.  and  Bry. 

This  disease  seems  to  be  common  on  cucumbers  in 
Florida,  Michigan,  and  in  Wisconsin.  It  has  been 

1  Rand,  F.  V.,  and  Enlows,  E.  M.  A.,  U.  S.  Dept.  of  Agr.,  Jour. 
Agr.  Research,  6  :  417-434,  1916. 


230  Diseases  of  Truck  Crops 

recently  studied  by  Smith  and  Bryan, x  who  described 
it  as  a  new  disease  occurring  in  the  Eastern  and 
Middle- Western  States. 

Symptoms.  The  trouble  is  characterized  by  angu- 
lar brown  spots  which  tear  or  drop  out  when  dry 
(fig.  40  b),  giving  a  ragged  appearance  to  the  infected 
leaves.  In  the  early  stages,  a  bacterial  exudate 
collects  in  drops  on  the  lower  surface  of  the  spots. 
These  exudates  usually  dry  and  become  whitish. 
It  seems  that  angular  leaf  spots  attack  only  the  foli- 
age but  rarely  the  fruit. 

The  Organism.  The  parasite  is  a  short  rod  with 
rounded  ends  (fig.  40  c),  occurring  singly,  or  in  pairs 
with  a  decided  constriction;  and  occasionally  in 
chains  of  twelve  individuals  or  more.  It  is  motile  by 
means  of  polar  flagella,  produces  capsules  on  agar 
and  milk;  no  spores,  and  no  gas  is  formed.  The  or- 
ganism completely  liquefies  gelatine  in  about  three 
or  four  weeks. 

DAMPING  OFF,  see  PYTHIUM,  p.  43. 

DOWNY  MILDEW 

Caused  by  Pseudoperono spora  cubensis  (B.  and  C.) 
Rost. 

Downy  mildew  is  prevalent  in  New  Jersey,  New 
York,  Florida,  Texas,  and  possibly  other  States.  It 

1  Smith,  E.  W.,  and  Bryan,  M.  K.,  U.  S.  Dept.  of  Agr.,  Jour.  Agr. 
Research,  6  :  465-476,  1915. 


FIG.  40.     CUCUMBER  DISEASES. 

a.  Mosaic,  b.  angular  leaf  spot  (after  Smith  and  Bryan),  c.  individual  germs  of 
Fseudomonas  lachrymans,  d.  downy  mildew  (Manns),  e.  conidiophore  and  conidia  of 
Plasmopara  cubensis,  f.  germinated  conidia  and  swarm  spore,  g.  germinated  swarm 
spores  (e.  to  g.  after  Clinton),  h.  anthracnose. 


Family  Cucurbitaceae  231 

attacks  cantaloupes,  gourds,  squashes,  pumpkins, 
and  watermelons. 

Symptoms.  The  disease  appears  as  yellowish  spots 
on  the  leaves,  which  have  no  definite  outline  (fig. 
40  d).  With  warm  moist  weather,  numerous  spots 
coalesce,  and  soon  the  affected  leaves  turn  yellow 
and  die.  With  cool  weather  the  spots  seem  to  spread 
less  rapidly.  The  disease  appears  to  work  on  the 
older  leaves,  beginning  on  those  on  the  center  of  the 
hill  and  working  outward.  With  infected  plants 
the  center  of  the  hill  is  clearly  marked  by  a  cluster 
of  yellow  leaves.  Diseased  plants  may  flower  pro- 
fusely, but  no  fruit  is  produced.  The  few  cucumbers 
which  set  are  small,  deformed,  and  unfit  for  the 
market. 

Downy  mildew  is  most  prevalent  in  August  with 
moderate  rainfall  and  hot  weather.  The  disease 
spreads  very  rapidly  and  a  large  cucumber  field 
may  be  a  total  loss  in  less  than  from  eight  to  ten 
days. 

The  Organism.  The  fungus  derives  its  food  from 
the  host  cells  by  means  of  suckers  or  haustoria.  The 
mycelium  is  hyaline,  non-septate ;  the  conidiophores 
(fig.  40  e)  arise  in  small  clusters  through  the  leaf 
stomata  and  are  branched  and  flexuous.  The 
zoosporangia  are  hyaline  but  slightly  violet,  tinted  in 
mass.  Germination  of  zoosporangia  is  by  means  of 
motile  zoospores  (fig.  40  f-g) .  The  oospore,  or  sexual 
fruiting  stage,  was  first  found  on  the  host  by  Ros- 
tovtsev.  Downy  mildew  may  be  kept  in  check  by 
spraying  with  Bordeaux  mixture. 


232  Diseases  of  Truck  Crops 

POWDERY  MILDEW 
Caused  by  Erysiphe  cichoracearum  D.  C. 

Powdery  mildew  of  cucumbers  is  not  a  serious 
trouble,  since  it  usually  attacks  plants  which  have 
somewhat  passed  their  usefulness.  Like  all  powdery 
mildews,  the  causative  fungus  grows  on  the  surface 
of  the  leaf,  giving  it  a  white  mealy  appearance. 
From  the  mycelium  are  produced  erect  threads  which 
bear  the  summer  spores  of  the  fungus.  According 
to  Humphrey, x  the  ascus  or  winter  stage  appears  as 
minute  dark-brown  rounded  capsules  enclosing  a 
group  of  spore  sacs  within  which  are  formed  the 
ascospores. 

ANTHRACNOSE  (fig.  40  h),  see  WATERMELON,  p.  240. 

ROOT  KNOT,  see  SQUASH,  p.  237. 

SPRAYING  CANTALOUPES  AND  CUCUMBERS 

Cantaloupes  and  cucumbers  cannot  always  be 
grown  profitably  unless  the  crops  are  sprayed.  It  is 
fortunate  that  most  of  the  foliage  and  fruit  diseases 
may  be  kept  in  check  by  spraying  with  Bordeaux 
mixture.  The  work  of  Orton2  and  others  has  shown 
that  not  only  does  spraying  control  the  various  dis- 
eases, but  viewed  from  the  point  of  view  of  dollars 
and  cents  it  undoubtably  pays. 

1  Humphrey,  J.  E.,  Massachusetts  Agr.  Expt.  Sta.  loth  Ann. 
Rept.:  225-226,  1892.  fcj 

2  Orton,  W.  A.,  U.  S.  Dept.  of  Agr.  Farm.  Bui.  231 :  5-24,  1905. 


Family  Cucurbitaceae  233 

Cucumbers  grown  for  pickles,  however,  should  not 
be  sprayed,  as  spraying  reduces  the  number  of  fruit, 
although  it  is  so  beneficial  for  fruit  which  are  to  be 
left  to  grow  to  market  size. 

For  an  area  less  than  one  acre,  a  small  hand  pump 
sprayer,  or  preferably  a  good  small  compressed-air 
sprayer  will  answer  the  purpose.  For  fields  of  one 
to  five  acres  a  barrel  sprayer  is  recommended.  For 
fields  above  five  acres  or  more,  a  good  power  sprayer 
must  be  able  to  apply  at  least  one  hundred  gallons 
per  acre.  To  do  thorough  spraying,  a  slow  walking 
team  should  be  chosen,  but  the  pump  should  be  geared 
correspondingly  high  so  as  to  maintain  full  pressure 
at  a  low  speed. 

The  strength  of  Bordeaux  recommended  by  Orton 
as  safe  from  burning  is  a  3-6-50  formula.  From  the 
writer's  experience,  he  would  not  advise  using  formu- 
las stronger  than  this,  especially  under  Southern 
climatic  conditions.  The  time  to  spray  first  is  when 
the  vines  begin  to  run.  The  number  of  succeeding 
applications  should  be  governed  by  climatic  condi- 
tions. In  damp  warm  weather,  spraying  should  be  re- 
peated every  second  or  third  week.  The  object  is  to 
keep  all  growing  parts  of  the  plant  thoroughly  covered 
with  the  fungicide.  For  further  directions  on  spraying 
and  the  preparations  of  the  ingredients,  see  p.  361. 

In  some  seasons,  the  melon  louse,  Aphis  gossypii, 

causes  great  damage  to  cantaloupes  and  cucumbers. 

The  pest  sucks  the  life  of  the  plant  by  feeding  on  its 

juices.     Durst1  recommends  spraying  with  "  Black 

1  Durst,  C.  E.,  Illinois  Agr.  Expt.  Sta.  Bui.  174  : 321-334,  1914. 


234  Diseases  of  Truck  Crops 

Leaf  40,"  used  at  the  rate  of  one  part  to  one  thousand 
of  water.  This  will  control  the  aphids.  "  Black 
Leaf  40"  readily  mixes  with  Bordeaux  mixture.  To 
control  both  fungus  and  plant  lice,  add  to  every  one 
hundred  gallons  of  Bordeaux  one  pint  of  "Black 
Leaf  40."  To  control  chewing  insects,  such  as  the 
cucumber  striped  beetle  or  caterpillars  feeding  on 
the  plants,  add  to  each  one  hundred  gallons  of  Bor- 
deaux three  pounds  of  powdered  arsenate  of  lead. 

DISEASES  OF  THE  CITRON  (Citrullus  vulgaris) 

Citrons  are  not  grown  commercially.  They  are 
found  as  weeds  in  melon  patches  or  anywhere  in  the 
farm  where  permitted.  The  citron  is  a  very  hardy 
plant,  and  it  is  subject  to  but  few  diseases. 

ANTHRACNOSE,  see  WATERMELON,  p.  240. 

LEAF  SPOT,  see  WATERMELON,  p.  243. 

GOURD  DISEASE,  see  SQUASH,  p.  234. 

MUSKMELON  DISEASES,  see  CANTALOUPES,  p.  219. 

PUMPKIN  DISEASES,  see  SQUASH,  p.  234. 

DISEASES  OF  THE  SQUASH  (Cucurbita 
maxima,  C.  pepo,  and  C.  Moschata) 

Squashes,  with  but  few  exceptions,  are  subject  to 
the  same  diseases  as  affect  the  cantaloupe  and  the  cu- 
cumber. Squashes  are  usually  grown  for  local  mar- 
kets, and  because  of  their  diseases  in  many  places 
their  culture  has  been  abandoned. 

BACTERIAL  WILT,  see  CUCUMBER,  p.  229. 


.    FIG.  41.    SQUASH  DISEASES. 

a.  Showing  squash  blossoms  invaded  by  the  fungus  Choanophora  cucurbitarum, 
b.  squash  entirely  rotted  by  the  Choanophora  fungus,  c.  young  conidiophore  or 
Choanophora  with  ramuli  developing  on  the  primary  vesicle,  d.  mature  capitulum 
covered  with  a  layer  of  conidia,  e.  conidia,  /.  sporangia  and  columella,  g.  sporangio 
spores  with  tufts  of  hair-like  appendages,  h.  mature  zygospore  (a,  c.  to  h.  after 
Wolf),  *.  Fusarium  wilt  of  young  squash  plants,  j.  Rhizopus  rot. 


Family  Cucurbitaceae  235 

FRUIT  ROT 

Caused  by  Choanophora  cucurbitarum  (B.  and  Rav.) 
Thax. 

Fruit  rot  is  a  common  disease  of  the  summer 
squashes.  It  has  been  found  in  North  and  South 
Carolina,  Massachusetts,  New  York,  Ohio,  Michigan, 
Connecticut,  Florida,  and  Texas.  The  disease  is  of 
little  importance  in  dry  seasons.  It  is,  however, 
favored  by  conditions  of  high  humidity  and  excessive 
rainfall,  or  by  heavy  dews  at  night. 

Symptoms.  It  usually  attacks  the  flowers,  or 
especially  the  remnants,  of  the  old  calyx  (fig.  41  a). 
The  latter  when  affected  become  shriveled  and  cov- 
ered with  a  thick  crop  of  brown  conidiophores  of  the 
causative  fungus.  From  the  floral  parts,  the  my- 
celium works  downward  and  into  the  young  squash, 
which  wilts  very  rapidly,  turning  into  a  soft  rot  and 
later  covered  by  a  gray  growth  of  conidiophores 
(fig.  41  b).  As  far  as  is  known,  the  fungus  does  not 
attack  any  other  part  of  the  squash  plant  except  the 
floral  parts  and  the  fruit. 

The  varieties  of  squash  most  affected  by  fruit  rot 
are  the  "patty  pan"  types,  commonly  known  as 
cymblings.  Wolf1  has  found  Choanophora  cucurbi- 
tarum on  fading  flowers  of  cucumber,  Althea,  scarlet 
hibiscus,  okra,  and  cotton. 

The  Fungus.  The  conidiophores  when  young  are 
whitish,  but  at  maturity  take  on  a  metallic  luster. 

1  Wolf,  F.  A.,  U.  S.  Dept.  of  Agr.,  Jour.  Agr.  Research,  8  : 319-328, 
1917. 


236          Diseases  of  Truck  Crops 

The  top  end  is  broadest,  becoming  dilated  into  a 
caputate  vesicle.  From  this  head  are  produced  from 
a  few  to  a  dozen  small  branches,  the  tips  of  each  in 
turn  becoming  vesicular  (fig.  41  c).  Each  vesicle 
now  becomes  covered  with  a  dense  layer  of  conidia 
(fig.  41  d).  The  latter  are  light  to  reddish  brown 
in  color  (fig.  41  e).  The  conidia  germinate  by  means 
of  a  germ  tube.  Sporangia  are  formed  in  pure 
culture  but  not  on  the  host.  Sporangia  are  first 
evident  as  white  pendant  enlargements,  becoming 
separated  from  the  sporangiophore  by  a  globular 
columella  (fig.  41  f).  Mature  sporangiospores  are 
larger  than  the  conidia,  are  smooth,  and  possess 
terminal  hyaline  appendages  (fig.  41  g).  The  spores 
germinate  by  means  of  the  germ  tube,  as  is  the  case 
with  the  conidia.  Chlamydospores  are  not  uncom- 
mon and  they  have  often  been  observed  during  the 
winter.  The  formation  of  zygospores  is  a  common 
occurrence  on  culture  media,  but  not  on  the  host. 
The  method  of  zygospore  formation  and  germina- 
tion has  not  as  yet  been  definitely  worked  out. 

Control.  The  spores  of  Choanophora  cucurbitarum 
are  undoubtedly  carried  from  flower  to  flower  by 
insects.  Spraying,  as  outlined  for  cucumbers,  is  also 
recommended  for  the  squash,  p.  232. 

SOFT  ROT 
Caused  by  Rhizopus  nigricans  Ehr. 

Soft  rot  very  often  cannot  be  distinguished  from 
the  fruit  rot  above  mentioned  (fig.  41  j).  The  symp- 


Family  Cucurbitaceae  237 

toms  in  both  diseases  are  very  much  alike.  The  only 
disparity  consists  in  the  difference  of  the  two  causa- 
tive organisms.  For  a  further  study  of  Rhizopus 
nigricans,  see  soft  and  ring  rot  of  the  sweet  potato, 
pp.  156-159. 

POWDERY  MILDEW,  see  CUCUMBER,  p.  232. 

ANTHRACNOSE,  see  WATERMELON,  p.  240. 

LEAF  SPOT,  see  CANTALOUPE,  p.  224. 

WILT  OR  YELLOWS 
Caused  by  Fusarium  cucurbitcz  Taub. x 

One  of  the  greatest  drawbacks  to  squash  culture 
in  many  of  the  Southern  States,  especially  in  Texas, 
is  a  disease  known  as  wilt  (fig.  41  i)  or  yellows.  The 
symptoms  of  the  squash  wilt  are  identical  with  those  of 
the  watermelon  wilt,  see  p.  244.  However,  the  organ- 
ism F.  cucurbitcE  is  different  and  distinct  from  the  three 
species  of  Fusarium  which  are  capable  of  producing  a 
wilt  on  watermelon.  The  name  Fusarium  cucurbi- 
ts n.  sp.  is  therefore  given  to  the  squash  wilt 
organism  to  distinguish  it  from  other  species  of  Fusa- 
rium. From  investigations  by  the  writer  there  has 
been  found  no  variety  which  is  resistant  to  wilt.  On 
the  other  hand,  the  pumpkin  Cucurbita  pepo,  and  the 
"sugar  through"  gourd  Lagenaria  vulgaris  will 
thrive  in  soils  where  squashes  are  known  to  fail  from 
wilt.  Watermelons,  cowpeas,  cotton,  and  okra  will 
also  thrive  well  in  Fusarium-sick  soil  of  squashes. 
Occasionally  it  is  found  that  cowpeas  and  okra  will 

1  From  unpublished  data  of  the  author. 


238          Diseases  of  Truck  Crops 

die  from  a  wilt  in  the  same  field  where  squashes  are 
not  thriving.  However,  the  writer  has  been  able  to 
prove  that  the  wilt  of  cowpea  and  okra  are  diseases 
caused  by  two  distinct  species  of  Fusarium,  and  that 
both  of  these  parasites  may  be  found  in  the  same  field 
also  infected  with  Fusarium  cucurbita  of  the  squash. 

ROOT  ROT,  see  RHIZOCTONIA,  p.  45. 

ROOT  KNOT,  see  NEMATODE,  p.  49. 

DISEASES  OF  THE  WATERMELON  (Citrullus 
vulgaris) 

MALNUTRITION 
Cause,  physiological. 

Malnutrition  seems  to  occur  in  fields  deficient  in 
potash.  The  trouble  is  apparently  new,  brought 
about  by  the  scarcity  of  potash,  due  to  war  conditions. 
The  disease  is  characterized  by  light  brown  spots 
located  around  the  veins  and  margins  of  the  leaf. 
The  disease  must  be  further  investigated  before  re- 
medial measures  may  be  suggested. 

BACTERIAL  WILT,  see  CANTALOUPE,  p.  219. 

DOWNY  MILDEW,  see  CUCUMBER,  p.  230. 

POWDERY  MILDEW,  see  CUCUMBER,  p.  222. 

HONEY  DEW  OR  SOOTY  MOLD 
Caused  by  CAPNODIUM  sp. 

Watermelon  stems,  petioles,  and  leaves  often  be- 
come coated  with  a  black  sooty  growth.  This  is 


FIG.  42.     WATERMELON  DISEASES. 

a.  Stem  end  rot  (after  Meier),  b.  anthracnose  of  foliage,  c.  anthracnose  on  fruit, 
d.  Fusarium  wilt  of  young  seedlings,  e.  blossom  end  rot. 


Family  Cucurbitaceae  239 

more  abundant  on  the  older  leaves,  or  even  on  the 
nearly  mature  melon  fruit.  Although  the  mold  seems 
to  grow  superficially  on  the  outside  of  the  affected 
parts,  the  result  is  a  general  suffocation,  since  sun- 
light and  free  circulation  of  air  are  interfered  with. 
Sooty  mold  undoubtedly  grows  on  the  sweetish  ex- 
creta of  plant  lice,  and  is  severest  during  seasons  of 
Aphis  epidemics.  Spraying  with  ''Black  Leaf  40" 
to  control  Aphis  gossypii  will  also  control  sooty  mold. 
The  fungus  Capnodium  apparently  does  not  derive 
any  nourishment  from  the  watermelon,  but  from  the 
honey  excreted  by  plant  lice. 
MYCOSPHAERELLA  WILT,  see  CANTALOUPE,  p.  222. 

STEM  END  ROT 
Caused  by  Diplodia  tubericola  (E.  and  E.)  Taub. 

This  disease  was  first  studied  by  Meier1  who  found 
the  trouble  confined  mostly  to  watermelons  in  transit. 
Many  carloads  when  reaching  their  destination 
showed  a  loss  from  it  of  75%  to  95%. 

Symptoms.  The  first  indication  of  the  rot  is  a 
browning  and  shriveling  of  the  stem  end  of  the  fruit 
(fig.  42  a).  Rotting  begins  at  the  point  of  attach- 
ment of  the  melon  to  the  stem  of  the  plant.  The 
flesh  of  the  affected  melon  blackens,  softens,  and 
becomes  watersoaked  and  then  slimy.  Such  melons 
when  left  to  themselves  become  black,  wrinkled,  and 
mummified.  Infection  undoubtedly  must  take  place 

1  Meier,  F.C.,  U.S.Dept.  of  Agr.,  Journal  ofAgr.  Research,  6  : 149- 
152,  1916. 


240          Diseases  of  Truck  Crops 

in  the  field  before  loading.  The  disease  incubates 
while  in  transit  and  makes  its  appearance  when 
the  assigned  shipment  reaches  its  final  destina- 
tion. 

The  Organism.  The  organism  which  catfses  stem 
end  rot  of  watermelon  is  the  same  which  is  re- 
sponsible for  the  Java  black  rot  of  the  sweet 
potato.  This  has  been  proved  by  Meier  and  by 
the  writer.  For  further  discussion  of  the  fungus, 
see  p.  165. 

Control.  Diplodia  tubericola  may  easily  live  over 
from  year  to  year  on  the  cull  melons  left  in  the  field, 
on  the  sweet  potato  refuse  or  on  any  other  trash. 
Therefore  infected  culls  and  refuse  should  be  de- 
stroyed. In  hauling  melons  to  the  car,  only  wagons 
with  springs  should  be  used.  The  cars  should  be 
carefully  swept  and  cleaned  before  loading.  Rough 
handling  or  bruising  should  be  avoided  as  much  as 
possible  and  only  sound  melons  should  be  loaded  in 
the  car.  The  fruit  should  be  carefully  packed  so  as 
to  avoid  bruising  from  shaking  when  the  cars  are 
moved. 

ANTHRACNOSE 

Caused  by  Cottetotrichum  lagenarium  (Pass.)  E. 
andH. 

Anthracnose  is  a  disease  the  seriousness  of  which 
depends  on  weather  conditions,  it  thriving  best  dur- 
ing hot,  moist  weather.  It  is  very  prevalent  in  many 


FIG.  43.     WATERMELON  ANTHRACNOSE. 

a.  Healthy  watermelon  hill,  b.  field  destroyed  by  anthracnose. 


Family  Cucurbitaceae  241 

States,  although  it  has  not  as  yet  been  found  to  be 
serious  in  Texas. 

Symptoms.  It  attacks  all  parts  of  the  plant  except 
the  root.  On  the  stems  it  causes  watersoaked 
spots,  which  in  time  turn  brownish  and  become 
depressed  and  cracked.  On  the  leaves,  somewhat 
circular  dark  spots  become  so  numerous  as  to  involve 
the  entire  area  (fig.  42  b),  resulting  in  the  death  of  the 
leaf.  Diseased  leaves  soon  crinkle,  turn  black,  and 
have  the  appearance  of  being  burned  by  fire.  On  the 
fruit,  anthracnose  is  manifested  on  the  rind  as  cir- 
cular deep  depressions  (fig.  42  c)  which  soon  become 
covered  with  a  salmon-colored  coat  made  up  of  the 
spores  of  the  fungus.  Ordinarily  the  spots  do  not 
go  deeper  than  the  rind.  Under  improper  methods 
of  shipping,  the  fungus  eats  into  and  penetrates  the 
flesh  of  the  melon  which  decays  rapidly.  Anthrac- 
nose reduces  the  market  value  of  the  melons,  and 
makes  shipping  a  very  risky  affair,  since  the  disease 
readily  spreads  in  the  car.  This  is  especially  true 
when  the  cars  are  sidetracked  and  held  too  long  in 
transit.  In  the  field,  anthracnose  may  ruin  the 
entire  stand  (fig.  43  a-b). 

Besides  attacking  watermelons,  anthracnose  also 
attacks  cucumbers,  cantaloupes,  citrons,  and  gourds. 
The  disease  is  not  usually  serious  on  new  land;  but 
on  land  where  watermelons  have  been  grown  in  suc- 
cession for  a  period  of  years,  or  where  melons  fol- 
lowed cantaloupes  or  cucumbers,  the  disease  may 
become  serious. 

The  Organism.     In  structure,  Colletotrichum  lage- 

16 


242  Diseases  of  Truck  Crops 

narium  resembles  the  organism  of  bean  anthracnose, 
see  p.  263.  The  watermelon  fungus  has  a  peculiar 
ability  to  remain  dormant  during  dry  weather;  but 
it  is  easily  revived  by  rains  or  dew.  This  is  why 
anthracnose  often  appears  overnight  in  carloads 
shipped  to  market.  The  fruits  of  the  fungus  are 
borne  in  masses  on  the  pustules  which  take  on  a 
salmon  color.  The  spores  are  typical  of  all  Colleto- 
trichums — that  is,  oval,  one-celled,  and  hyaline.  The 
setse  in  C.  lagenarium  are  not  very  plentiful.  In 
pure  culture  it  resembles  C.  lindemuthianum;  how- 
ever, pathologically  it  is  distinct  from  the  latter,  since 
numerous  attempts  by  the  writer  and  by  others 
have  failed  to  infect  growing  bean  plants  with  the 
watermelon  anthracnose  or  the  watermelon  with 
that  of  the  bean. 

Control.  With  this  disease,  prevention  is,  of  course, 
the  cheapest  method  of  control.  From  what  has 
been  said,  it  is  evident  that  it  is  never  wise  to  grow 
watermelons  too  long  on  the  same  land.  In  prevent- 
ing the  disease  from  gaining  a  foothold  on  the  land, 
a  three-year  rotation  will  probably  answer  the  pur- 
pose. On  lands  in  which  the  crop  has  suffered  severely 
from  anthracnose,  a  longer  rotation,  say  six  years, 
may  be  necessary.  The  disease  is  carried  over  in  the 
soil  from  year  to  year  on  the  dead  leaves,  vines,  and 
diseased  fruits  which  remain  in  the  field.  These, 
therefore,  should  never  be  plowed,  but  destroyed 
by  fire.  Spraying,  too,  will  help  to  keep  the  disease 
in  check.  Bordeaux  in  this  case  is  the  standard 
fungicide  to  use.  However,  it  should  be  borne  in 


Family  Cucurbitaceae  243 

mind  that  watermelon  leaves  are  very  tender  and 
hence  susceptible  to  injury.  Recent  experiments  by 
the  writer  have  shown  that  a  very  weak  Bordeaux 
with  a  large  excess  of  lime  should  be  used  in  order  to 
prevent  the  burning  of  the  foliage.  Where  this  pre- 
caution is  overlooked,  a  greater  injury  will  result 
from  the  use  of  the  fungicide  than  from  the  disease 
itself  (fig.  44  b).  A  Bordeaux  made  up  of  three 
pounds  of  copper  sulphate,  eight  pounds  of  lime,  and 
fifty  gallons  of  water,  to  which  is  added  one  pound 
of  powdered  arsenate  of  lead,  will  answer  the 
purpose  well.  The  lead  arsenate  in  this  case  is 
used  against  various  caterpillars  which  often  feed 
on  the  leaves  of  the  plants.  Paris  green  should 
not  be  used  because  of  its  tendency  to  burn  the 
foliage. 
CERCOSPORA  LEAF  SPOT,  see  CANTALOUPE,  p.  224. 

CERCOSPORA  LEAF  SPOT 
Caused  by  Cercospora  citrulUna  Cke. 

This  form  of  leaf  spot  is  induced  by  a  species  of 
Cercospora  different  from  that  which  attacks  canta- 
loupes. The  trouble  usually  appears  on  the  oldest 
leaves  as  circular  spots  bordered  by  a  dark  brown 
or  purplish  zone  beyond  which  is  an  area  of  yellow. 
The  mature  spots  have  gray  centers.  This  form  of 
leaf  spot  is  prevalent  on  watermelons  in  Texas.  It 
may  be  controlled  by  spraying  in  the  same  way  as 
recommended  for  anthracnose. 


244  Diseases  of  Truck  Crops 

VINE  WILT  OR  YELLOWS 

Caused  by  Fusarium  niveum  Ew.  Sm.;  Fusarium 
citrulli  Taub.1;  Fusarium  Poolensis  Taub.a 

Failure  of  the  watermelon  crop  in  many  of  the 
Southern  States  may  be  safely  attributed  to  wilt. 
There  is  no  other  watermelon  disease  that  is  so  diffi- 
cult to  control.  The  reason  is  obvious.  The  causa- 
tive fungi  live  in  the  soil  as  semi-saprophytes.  The 
longer  watermelons  are  grown  on  that  soil,  the  worse 
the  disease  becomes.  In  severe  cases  the  crop  may 
be  a  total  failure,  or  the  loss  run  as  high  as  fifty  per 
cent,  of  the  crop. 

Symptoms.  There  is  no  outside  spotting  nor  are 
there  any  lesions  to  indicate  the  presence  of  wilt. 
The  source  of  the  trouble  is  confined  entirely  to  the 
interior  of  the  roots  and  stems.  The  leaves  of  an 
affected  plant  suddenly  droop;  this  is  followed  by  a 
rapid  wilting  of  all  the  vines  in  that  hill  (fig.  44  a) 
from  which  they  never  revive.  The  wilting  is  more 
intensified  during  a  warm  dry  spell.  Occasionally 
only  one  or  two  vines  in  the  hill  wilt  and  die  while 
others  in  the  same  hill  remain  alive  for  some  time 
before  succumbing  to  the  disease.  In  pulling  out  a 
plant  that  has  recently  died,  its  roots  are  found  to  be 
sound  with  the  exception  of  a  dull  yellowish  color 
which  the  exterior  exhibits.  In  splitting  open  a  vine 

1  From  unpublished  data  by  the  writer,  the  organism  was  carried 
as  Fusarium  No.  106. 

2  The  organism  was  carried  as  Fusarium  No.  116. 


FIG.  44.     WATERMELON  DISEASES. 

a    Wilt  (Fusarium  niveuni),   b.  Bordeaux  injury,  c.  Tom  Watson, 
an  ideal  shipping  melon,  d.  macroconidia  of  Fusarium  niveum. 


Family  Cucurbitaceae  245 

or  root  of  the  diseased  plant,  its  interior  fibrovascular 
bundles  will  be  browned.  The  browning  indicates 
the  presence  of  the  parasite. 

Wilt  is  not  always  confined  to  the  older  plants. 
In  badly  infected  fields  young  seedlings  begin  to  die 
at  an  early  age  (fig.  42  d),  resulting  in  a  very  poor 
stand.  From  the  investigations  of  the  writer,  it  has 
been  found  that  Fusarium  citrulli  is  more  active  on 
seedlings  than  are  the  other  two  species  of  Fusarium. 
This,  however,  is  not  intended  to  convey  the  idea  that 
F.  niveum  and  F.  Poolensis  are  not  capable  of  pro- 
ducing wilt  on  the  younger  seedlings. 

The  Organisms.  The  three  species  of  Fusarium 
which  produce  wilt  of  watermelon  may  be  readily 
distinguished  when  grown  in  flasks  on  cornmeal. 
Fusarium  citrulli  is  entirely  different  from  the  two 
others  in  that  it  forms  a  glistening,  flat,  compact, 
flesh-colored  dry  growth  confined  to  the  surface  of 
the  cornmeal.  Growth  is  slow,  and  no  color  is  pro- 
duced in  the  substratum  for  a  considerable  time, 
about  two  months  or  more.  Fusarium  Poolensis  at 
first  greatly  resembles  F.  niveum  in  growth  and  in 
color.  Later,  however,  F.  Poolensis  takes  on  a  deep 
blue  to  almost  indigo  which  is  retained  indefinitely. 
The  three  species  of  Fusarium  have  been  definitely 
proved  by  the  writer  to  be  the  cause  of  the  water- 
melon wilt.  Infection  can  take  place  only  on  water- 
melons and  not  on  any  other  cucurbit  hosts,  nor  on 
cotton,  okra,  or  cowpea,  the  wilts  on  all  of  which  are 
caused  by  different  species  of  Fusarium.  It  is  possible, 
however,  that  a  sick  watermelon  field  may  also  be 


246  Diseases  of  Truck  Crops 

infected  with  Fusarium  cucurbita,  thus  making  it 
also  sick  to  squashes. 

Control.  Since  the  disease  works  in  the  interior  of 
the  plant,  it  is  obvious  that  spraying  would  be  of 
little  help.  Rotation  of  crops  is  the  only  practical 
method  of  control.  It  usually  takes  from  two  to 
three  years  for  wilt  to  establish  itself  very  seriously 
in  the  field.  Because  of  this,  growers  often  fail  to 
appreciate  its  importance  until  too  late.  Any 
possible  profits  made  during  the  time  the  crop  has 
been  grown  in  succession  on  the  same  land  are  more 
than  offset  by  the  fact  that  the  infected  soil  is  ren- 
dered sick  and  unfit  for  watermelons  for  ten  years 
or  longer.  Watermelon  plants  suffering  from  wilt 
should  never  be  plowed  under,  but  should  be  pulled 
out,  dried,  and  burned.  Wilt  may  be  spread  by 
cattle  and  horses  which  are  allowed  to  pasture  in  the 
sick  melon  patches,  and  then  brought  to  healthy 
fields.  Finally  a  method  which  promises  great  re- 
lief is  the  development  of  resistant  varieties  which 
are  able  to  grow  in  sick  soils.  The  United  States 
Department  of  Agriculture  has  developed  a  wilt  re- 
sistant variety  named  Conqueror.  This  is  a  cross 
between  the  citron  and  the  Eden.  The  Conqueror, 
however,  is  not  as  yet  popular  with  the  market  be- 
cause of  the  uncertain  qualities  of  the  citron  which  it 
still  has.  Resistant  varieties  may  no  doubt  be  ob- 
tained by  selection  with  the  best  commercial  vari- 
eties. For  methods  of  selection  for  resistance  see 

P-  374- 
ROOT  KNOT,  see  NEMATODE,  p.  49. 


Family  Cucurbitaceae  247 

FRUIT  ROT 
Caused  by  Sclerotium  Rolfsii  Sacc. 

This  form  of  rot  is  seldom  serious  enough  to  war- 
rant any  treatment.  The  fungus  does  not  seem  to 
find  the  watermelon  fruit  as  suitable  a  host  as  the 
cantaloupe.  On  watermelons,  rotting  starts  at  a 
bruise  and  at  points  where  the  melon  touches  the 
ground.  Decay  is  slow  and  is  always  indicated  by  a 
cottony  growth  at  the  rotted  area. 

BLOSSOM  END  ROT 
Cause:  probably  due  to  fungi. 

This  is  a  disease  which  attacks  the  blossom  end  of 
the  fruit  (fig.  42  e)  and  causes  a  dry  rot,  but  which 
does  not  usually  penetrate  very  deep.  Nevertheless, 
affected  melons  are  unfit  for  the  market,  although 
they  ripen  earlier  and  have  a  much  sweeter  taste. 
The  cause  of  this  trouble  is  as  yet  unknown.  How- 
ever, numerous  observations  seem  to  indicate  that 
with  at  least  one  form  of  blossom  end  rot  it  seems  to 
be  brought  about  by  a  dry  spell  and  a  lack  of  mois- 
ture in  the  soil.  This  is  especially  the  case  in  fields 
where  coarse  manure  is  used  instead  of  good  compost. 
In  dry  seasons,  the  coarse  manure  fails  to  decompose 
properly  and,  at  the  same  time,  dries,  and  hence  re- 
sults in  injury  to  the  fruit.  To  prevent  this,  so 
far  as  possible,  only  well  rotted  manure  should  be 


248  Diseases  of  Truck  Crops 

used.  If  the  coarser  manure  has  to  be  used,  care 
should  be  taken  to  apply  it  from  four  to  eight  weeks 
before  planting,  thus  giving  it  ample  time  to  decom- 
pose. To  have  the  greatest  effect,  manure  should 
be  applied  as  deep  in  the  furrows  as  possible,  since  the 
tap-root  grows  very  deep  in  the  soil.  It  should  be 
remembered  that  the  watermelon  plant  has  numer- 
ous long  secondary  roots  which  are  heavy  feeders 
and  which  do  not  benefit  from  manure  if  it  is  applied 
in  the  center  of  the  hill.  Such  superficial  application, 
therefore,  often  results  in  starved  plants,  which  be- 
come further  weakened  by  spells  of  dry  weather,  or 
by  other  unfavorable  conditions.  To  obviate  this 
condition,  some  chemical  fertilizer  should  be  applied 
broadcast.  The  amount  of  manure  necessary  for 
one  acre  is  about  seven  tons,  applied  at  the  rate  of 
one  good  forkful  to  each  hill.  In  connection  with 
this,  about  four  hundred  pounds  of  well  balanced 
fertilizer  should  also  be  worked  in.  In  very  dry 
seasons,  small  amounts  of  nitrate  of  soda,  applied 
broadcast,  will  decidedly  benefit  the  plants.  The 
aim  in  fertilizing  should  be  to  supply  sufficient  humus 
to  the  soil,  thus  also  taking  care  of  the  soil  moisture 
at  a  time  when  the  plant  needs  it  most.  Moreover, 
the  use  of  proper  food  supply  will  result  in  more 
vigorous  plants,  with  an  abundance  of  foliage  protect- 
ing the  plants  from  burning  and,  at  the  same  time, 
reducing  blossom  end  rot. 

There  are  other  forms  of  blossom  end  rots.  Some 
may  possibly  be  attributed  to  imperfect  fertilization 
or  weak  pollen,  while  others  are  undoubtedly  caused 


Family  Cucurbitaceae  249 

by  parasitic  bacteria  and  fungi.  However,  without 
further  knowledge  it  is  impossible  to  suggest  other 
methods  of  control.  The  best  shipping  melon  is 
the  Tom  Watson  (fig.  44  c).  This  melon,  however, 
is  no  less  susceptible  to  diseases  than  any  other 
variety  grown  under  similar  field  conditions. 

WEEDS 

The  wild  cucumber  Micrampelis  (or  Echinveyster) 
lobate  is  subject  to  cucumber  mosaic  and  to  bacte- 
rial wilt.  With  this  exception  no  cucurbit  weeds  are 
subject  to  the  diseases  which  attack  the  cultivated 
species. 


CHAPTER  XV 

FAMILY  GRAMINE^E 

OF  this  great  family  the  only  crop  that  concerns 
the  trucker  and  gardener  is  sweet  corn.  This  is 
grown  to  a  great  extent  in  the  more  northern  States. 
In  the  South,  the  ordinary  field  corn  is  grown  instead 
of  sweet  corn  and  is  sold  for  "roasting  ears"  or  on  the 
cob  in  the  milky  stage.  The  present  discussion  will 
limit  itself  to  sweet  corn  only.  It  is  estimated  in  the 
Thirteenth  United  States  Census  that  the  total  area 
of  sweet  corn  in  the  United  States  in  1909  was 
178,224  acres  and  the  crop  was  valued  at  $2,719,340. 
The  States  ranked  according  to  area  in  sweet  corn 
were:  New  York,  Illinois,  Maryland,  Ohio,  Iowa, 
Pennsylvania,  New  Jersey,  Maine,  Indiana,  Michi- 
gan, Massachusetts,  Wisconsin,  Kansas,  Nebraska, 
Missouri,  California,  Minnesota,  Virginia,  Connecti- 
cut, Delaware,  Louisiana,  Vermont,  and  Kentucky. 
States  with  less  than  one  thousand  acres  are  omitted. 

DISEASES  OF  THE  SWEET  CORN  (Zea  Mays) 

Although  corn  is  considered  a  hardy  plant,  it  is 
nevertheless  subject  to  numerous  diseases.  Of  the 

250 


FIG.  45.     SWEET  CORN  DISEASES. 

a.  Bacterial  blight,  b.  individual  blight  organisms  (a.  to  b.  after  F.  C.  Stewart), 
c.  smut,  d.  smut  spores,  e.  and/,  germinating  spores  of  Ustilago  zece(d.  to/,  after  J.  B. 
S.  Norton). 


Family  Gramineae  251 

sweet   corn   but   three   diseases   need   concern   the 
trucker. 

BACTERIAL  WILT 
Caused  by  Pseudomonas  Stewarti  Erw.  Sm. 

Bacterial  wilt  is  perhaps  one  of  the  most  serious 
diseases  of  sweet  corn.  The  trouble  is  very  prevalent 
in  Long  Island,  New  York,  where  it  was  first  studied 
by  Stewart.1  It  is  also  prevalent  in  New  Jersey, 
Maryland,  West  Virginia,  Ohio,  Iowa,  Illinois,  and 
probably  many  other  States. 

Symptoms.  Bacterial  wilt  has  been  carefully 
studied  by  Dr.  Erwin  P.  Smith, 2  who  finds  that  the 
symptoms  of  this  disease  are  very  distinctive.  The 
first  mark  on  good  sized  plants  is  a  drying  out  and 
whitening  of  the  tassel,  giving  the  top  of  the  plant 
a  peculiar  whitish  appearance.  Another  sign  is 
a  dwarfing  of  the  plant,  followed  by  a  drying  of  the 
basal  leaves  which  gradually  works  upwards  (fig. 
45  a) .  The  affected  leaf  dies  from  the  tip  downwards 
or  from  the  margin  inwards.  The  disease  often 
attacks  young  plants  and  even  seedlings,  in  which 
case  they  dry  and  die  out  at  an  early  stage.  If  an 
infected  plant  is  cut  across  the  stem,  we  find  a  yellow 
slime  oozing  out  from  the  bundles;  this  slime  is 
teeming  with  the  bacteria.  In  cutting  through  a 

1  Stewart,  F.  G.-,  New  York  (Geneva)  Agr.  Expt.  Sta.  Bui.  130  : 
424-439,  1897. 

2  Smith,  E.  P.,  Bacteria  in  Relation  to  Plant  Disease,  3  :  89-174, 
Washington,  D.  C. 


252  Diseases  of  Truck  Crops 

stem  longitudinally,  it  will  be  found  that  the  bundles 
from  which  the  yellow  slime  oozes  out  are  browned 
or  bright  yellow.  This  shows  that  the  germ  is  con- 
fined to  the  fibrovascular  bundles  of  the  stem  and 
leaves. 

The  Organism.  Pseudomonas  Stewarti  is  a  short 
rod  with  rounded  ends  (fig.  45  b).  It  occurs  singly, 
in  pairs,  or  fours,  and  moves  about  by  means  of  polar 
flagella.  It  grows  slowly  on  gelatine  without  lique- 
faction. On  agar  plates  it  grows  slowly,  forming 
small  round  colonies.  It  produces  no  gas  and  is 
strictly  aerobic;  the  organism  is  very  sensitive  to  light. 

Control.  It  is  likely  that  the  disease  is  carried  with 
the  seed.  Hence  the  latter  should  be  secured  from 
localities  free  from  wilt.  Before  planting,  seed 
should  be  disinfected  in  formaldehyde,  see  p.  99. 
Not  all  varieties  of  sweet  corn  are  equally  subject  to 
wilt;  hence  truckers  are  advised  to  try  to  develop 
a  resistant  strain  or  strains  of  commercial  varieties. 
On  the  methods  of  selection  for  resistance,  see  p.  374. 
Finally,  fields  badly  infected  should  be  rotated  and 
devoted  to  other  crops  for  about  three  to  four  years. 
As  far  as  is  known  the  disease  only  attacks  corn, 
so  other  cereals  may  be  used  in  the  system  of  ro- 
tation. 

SMUT 
Caused  by  Ustilago  zecz  (Beck.)  Ung. 

Corn  smut  is  different  from  any  smut  which  at- 
tacks other  cereals.  The  greatest  damage  is  experi- 


Family  Gramincae  253 

enced  when  the  disease  attacks  the  ear,  destroying  or 
rendering  it  useless  for  market  purposes. 

Symptoms.  Corn  smut  does  not  usually  make  its 
appearance  before  the  plants  are  about  three  or 
four  feet  high.  It  is  manifested  as  boils  which 
may  attack  any  part  of  the  leaves  (fig.  45  c),  stalks, 
tassels,  or  ears.  The  boils  are  whitish  to  glossy, 
then  purple,  finally  rupturing  and  liberating  a  black 
powdery  mass  of  the  spores  (chlamydospores)  of  the 
fungus. 

The  Organism.  Within  the  tissue  of  the  affected 
host  the  smut  mycelium  consists  of  short  slender 
branched  filaments  closely  interwoven.  These 
slender  filaments  swell,  gelatinize,  and  portions  of 
them  round  off  as  spores.  The  latter  retain  their 
vitality  for  more  than  one  year.  The  chlamydo- 
spores (fig.  45  d)  germinate  by  sending  out  a  tube 
which  in  turn  bears  true  conidia  (fig.  45  e,  f).  The 
latter  germinate  by  sending  out  a  tube  which  pene- 
trates the  host. 

Control.  Corn  smut  is  not  carried  with  the  seed 
as  is  the  case  with  oat  or  wheat  smut.  Seed  treat- 
ment in  this  case  will  therefore  be  useless.  The  dis- 
ease is  carried  with  the  manure  or  in  the  soil.  The 
best  remedy,  therefore,  is  to  cut  out  and  destroy  by 
fire  all  smut  boils  as  they  appear.  This  must  be 
done  before  the  boils  are  ruptured.  If  this  is  care- 
fully practiced  by  everyone  in  each  community  corn 
smut  will  soon  disappear.  Smutted  ears  or  stover 
should  never  be  fed  to  animals,  as  this  is  a  common 
way  of  infecting  the  manure  pile. 


254  Diseases  of  Truck  Crops 

RUST 

Caused  by  Puccinia  sorghi  Schw. 

Corn  rust  is  a  disease  which  is  of  restricted  dis- 
tribution and  which  is  never  serious  enough  to  war- 
rant treatment.  It  is  characterized  by  chocolate 
colored  pustules  on  the  leaves  and  leaf  sheaths.  The 
aecidium  of  this  rust  occurs  on  oxalis  and  is  known  as 
jEcidium  oxalidis  Thum.  The  uredo  and  puccinia 
stages  both  occur  on  the  corn. 

WEEDS 

So  far  as  is  known,  none  of  the  Graminaceous 
weeds  are  subject  to  the  three  diseases  of  the  sweet 
corn  here  mentioned.  Nevertheless,  weeds  should 
never  be  tolerated. 


CHAPTER  XVI 

FAMILY  LABIATE 

THIS  family  contains  numerous  plants  which  are 
of  very  slight  economic  importance.  If  grown  at  all, 
they  are  cultivated  on  a  very  small  scale,  and  sold 
for  condiments.  Many  of  them  are  tropical  or 
semi-tropical,  but  most  of  them  could  be  grown  in 
frames  or  indoors.  The  following  is  a  list  of  plants 
which  belong  to  the  Labiatae:  Balm,  catnip,  clary, 
horehound,  hyssop,  lavender,  mint,  peppermint, 
pennyroyal,  rosemary,  sage,  spearmint,  summer 
savory,  sweet  basil,  and  sweet  marjoram.  Of  all 
these  hosts,  peppermint  and  spearmint  alone  are 
extensively  grown  in  the  United  States.  The  vola- 
tile oil  distilled  from  these  plants  is  the  principal 
marketable  product,  although  there  is  also  a  limited 
demand  for  the  dried  herb,  especially  the  spearmint, 
which  is  used  as  a  culinary  herb  for  flavoring  sauces 
and  cooling  drinks.  Of  recent  years,  these  herbs 
have  come  into  extensive  use  for  flavoring  chewing 
gum  and  confectionery.  The  United  States,  Japan, 
Russia,  Germany,  and  England  produce  all  of  the 
peppermint  and  spearmint  oils.  Fleet x  has  estimated 

1  Fleet,  W.  V.,  U.  S.  Dcpt.  of  Agr.  Farm.  Bui.  694  :  1-12,  1915. 

255 


256          Diseases  of  Truck  Crops 

the  total  annual  production  of  these  oils  to  be  600,000 
pounds,  250,000  of  which  are  produced  in  the  United 
States.  Peppermint  and  spearmint  are  grown  in 
Wayne  County,  New  York,  and  in  a  few  northern 
counties  of  Ohio,  Maryland,  and  Indiana.  Accord- 
ing to  the  Thirteenth  Census  of  the  United  States 
the  1909  area  devoted  to  mint  in  America  was  es- 
timated at  8,195  acres.  The  total  crop  was  valued 
at  $253,000.  Of  the  States  growing  most  on  a  com- 
mercial scale  may  be  mentioned  Indiana,  Michigan, 
New  York,  and  Tennessee. 

DISEASES  OF  THE  BALM  (Melissa  officinalis) 

RUST 
Caused  by  Puccinia  menihcB  Pers. 

The  disease  attacks  about  thirty-five  members  of 
the  mint  family.  All  the  three  stages  i.  e.,  secidio- 
spores,  uredospores,  and  teleutospores,  occur  on  the 
same  host.  The  disease  is  characterized  by  brown 
sori  which  are  at  first  cinnamon  colored  and  later 
chestnut  brown.  Diseased  leaves  curl  and  dry  up. 
The  disease  is  not  sufficiently  important  to  warrant 
treatment. 

LEAF  SPOT 
Caused  by  Septoria  melisscz  Desm. 

The  disease  is  characterized  by  numerous  brownish 
spots  which  are  angular  and  apparently  limited  by  the 


Family  Labiatae  £57 

veins  of  the  leaves.  Leaf  spot  has  not  been  found  in 
the  United  States,  but  it  is  said  to  be  common  in 
Europe. 

DISEASES  OF  THE  CATNIP  (Nepeta  cataria) 

STEM  ROT 
Caused  by  Didymella  cataria  (C.  and  E.)  Sacc. 

This  trouble  causes  spots  on  the  stems.  The 
disease  was  first  found  in  New  Jersey,  but  it  is  of 
little  importance. 

LEAF  SPOT 

Caused  by  Septoria  nepeta  E.  and  E. 

Leaf  spot  is  characterized  by  purplish  brown  cir- 
cular spots  which  are  surrounded  by  a  band  of  deeper 
brown.  The  disease  was  first  found  in  Racine,  Wis- 
consin, and  is  apparently  prevalent  on  the  Canadian- 
American  border. 

STEM  ROT 

Caused  by  Diplodinia  herbicola  (B.  and  C.)  Sacc. 

Stem  rot  was  first  reported  from  Pennsylvania,  but 

it  is  of  no  economic  importance. 
17 


258  Diseases  of  Truck  Crops 

DISEASES  OF  THE  HOREHOUND  (Marrubium 
vulgare) 

POWDERY  MILDEW 
Caused  by  Erysiphe  gaLeopsidis  D.  C. 

Powdery  mildew  is  characterized  by  powdery 
white  patches  on  the  leaves  and  stems.  The  trouble 
is  not  known  to  occur  in  the  United  States. 

LEAF  SPOT 
Caused  by  Diplodia  herbarum  (Corda)  Lev. 

The  spots  are  roundish  to  irregular,  numerous, 
brownish  to  dark  in  color.  The  disease  attacks  the 
older  leaves,  causing  them  to  drop  off  prematurely. 

DISEASE  OF  THE  MINT 
RUST,  see  BALM,  p.  256. 

DISEASE   OF  THE  PEPPERMINT  (Mentha 
pepenta) 

Peppermint  is  a  very  hardy  plant.  With  the  ex- 
ception of  RUST  (see  BALM,  p.  256),  it  is  practically 
free  from  attacks  of  fungus  diseases.  The  same  is 
also  true  for  the  spearmint,  Mentha  viridis,  which  is 
known  to  be  attacked  by  the  same  rust  diseases  as 
the  balm  and  all  the  other  Labiatae.  As  far  as  we 
know  the  weeds  in  this  family  are  not  carriers  of 
diseases  which  concern  the  trucker. 


CHAPTER  XVII 

FAMILY  LEGUMINOS^E 

THIS  important  family  includes  crops  which  are 
greatly  valued  by  the  consumer.  Of  the  numerous 
legume  plants,  we  will  consider  only  those  which 
concern  the  trucker, — viz.,  bean,  lima  bean,  cowpea, 
and  the  garden  pea. 

According  to  the  Thirteenth  Census  of  the  United 
States,  the  total  area  devoted  to  dry  edible  beans 
in  the  United  States  in  1909  was  estimated  at  802,991 
acres,  and  the  total  crop  valued  at  $21,771,482. 
That  of  green  beans  was  53,610  acres,  the  total  crop 
valued  at  $2,844,951.  The  important  leading  bean 
States  are  Michigan,  California,  New  York,  New 
Mexico,  Kentucky,  and  Maine.  The  estimated  area 
in  dry  peas  in  1909  was  1,305,099  acres,  and  the  total 
crop  valued  at  $10,963,739;  while  the  area  for  green 
peas  was  7°>487  acres,  yielding  a  crop  valued  at 
$2,785,502.  The  States  ranked  according  to  largest 
area  devoted  to  peas x  were  as  follows :  South  Carolina, 
Georgia,  North  Carolina,  Michigan,  Alabama,  Wis- 
consin, Mississippi,  Arkansas,  Texas,  Illinois,  Tennes- 

1  In  the  Thirteenth  Census,  no  distinction  is  made  between  the 
garden  pea  and  the  cowpea. 

259 


260          Diseases  of  Truck  Crops 

see,  Louisiana,  Colorado,  Missouri,  Indiana,  Virginia, 
Kentucky,  Florida,  and  Oklahoma. 

DISEASES  OF  THE    BEAN  (Phaseolus  vulgaris) 

Bean  growers  annually  lose  heavily  from  various 
bean  diseases.  There  is  no  other  truck  crop,  potatoes 
excepted,  which  has  received  as  much  attention  from 
plant  pathologists  as  the  bean.  With  our  present 
knowledge,  many  of  the  diseases  may  be  controlled. 

BLIGHT 
Caused  by  Pseudomonas  phaseoli  Ew.  Sm. 

Symptoms.  If  the  weather  is  wet  during  planting 
time,  the  seed  may  rot  in  the  ground  and  never  germi- 
nate. At  other  times  the  root  of  the  young  seed- 
lings may  decay  and  the  result  will  be  a  very  poor 
and  uneven  stand.  In  dry  weather  a  better  germi- 
nation is  obtained,  but  the  disease  works  on  the  older 
plants  in  irregular  spots  in  the  field.  Due  to  the 
lack  of  a  normal  root  system,  the  affected  plants 
are  yellowed  and  wilted  at  daytime,  but  they  slowly 
revive  at  night.  Should  the  weather  become  muggy 
in  midsummer,  infected  fields  appear  as  though  they 
were  drenched  with  hot  grease,  the  leaves  having  a 
burned  appearance  (fig .  46  a) .  As  a  result ,  the  in j  ured 
plants  seem  to  make  a  desperate  attempt  to  produce 
new  foliage  which  in  turn  becomes  affected,  hence 
the  pods  cease  filling  and  ripening  is  very  uneven. 

In  carefully  examining  diseased  seed,  it  is  found  to 
be  yellowed  and  shriveled;  or,  in  light  cases  of  attack, 


FIG.  46.     BEAN  DISEASES. 

a.  Bacteriosis  on  leaf,  b.  bacteriosis  on  pods,  c.  individual  germs  of  bacteriosis 
(after  Smith),  d.  bean  plant  killed  by  streak  (b.  to  d.  after  Sackett),  e.  streak  on 
pods. 


Family  Leguminosse  261 

there  are  found  indefinite  yellow  spots  or  blotches. 
On  the  leaves  the  trouble  appears  as  watersoaked 
spots  which  later  are  amber  colored  (fig.  46  a).  On 
the  stems  and  pods  (fig.  46  b)  a  canker  is  formed 
which  somewhat  resembles  the  canker  produced  by 
Colletotrichum  lindemuthianum.  From  the  stem  the 
disease  works  down  to  the  main  root,  causing  it  to  rot. 

The  Organism.  Pseudomonas  phaseoli  is  a  short 
rod  rounded  at  both  ends,  motile  by  means  of  polar 
flagella.  It  liquefies  gelatin  slowly,  coagulates  milk, 
and  the  whey  separates  slowly  with  acidity. 

Control.     The  same  as  for  anthracnose,  p.  265. 

STREAK 
Cause,  Bacterial. 

Streak  is  a  disease  which  is  little  known.  It  has 
been  recently  studied  by  Sackett, J  although  the  cause 
has  not  been  definitely  determined.  The  trouble 
may  perhaps  be  the  same  as  the  streak  of  the  sweet 
pea,  caused  by  Bacillus  lathy ri  Manns  and  Taub. 

Streak  attacks  stems,  leaves,  and  pods  (fig.  46  d,e) 
of  the  bean  plant.  On  the  pod  and  on  the  leaves  the 
disease  appears  as  peculiar  rusty  to  orange  brown 
spattered  spots  which  run  down  in  streaks.  Dis- 
eased foliage  drops  off  prematurely,  giving  the  plant 
a  denuded  appearance.  For  methods  of  control,  see 
bean  anthracnose,  p.  265. 

DAMPING  OFF,  see  PYTHIUM,  p.  43. 

DOWNY  MILDEW,  see  LIMA  BEAN,  p.  267. 

1  Sackett,  W.  A.,  Colorado  Agr.  Expt.  Sta.  Bui.  226  : 27, 1917. 


262  Diseases  of  Truck  Crops 

RUST 
Caused  by  Uromyces  appendiculatus  (P.)  L. 

Rust  is  seldom  serious  enough  to  warrant  treat- 
ment. The  disease  attacks  all  parts  of  the  bean 
plant  except  the  roots.  On  the  foliage,  it  appears  as 
little  brown  pimples  or  sori  (fig.  47  a)  the  size  of  a 
pin's  head.  These  pimples  soon  appear  on  the  pods 
(fig.  47  b),  petioles,  and  stems,  being  more  numerous 
however  on  the  leaves  and  pods.  The  pimples  as 
they  get  older  turn  from  brown  to  black  in  color. 
The  powder  discharged  from  the  sori  is  made  up  of 
countless  numbers  of  the  fungus  spores.  Rust  does 
not  live  over  on  the  seed,  but  rather  on  the  dead  re- 
fuse of  the  bean  plants.  Bean  rust  has  the  aecidio- 
spores,  uredospores  (fig.  47  d),  and  teleutospores  (fig. 
47  c)  on  the  same  host. 

Clean  culture,  burning  of  trash  and  dead  plants, 
and  selection  of  resistant  strains  or  varieties  is  re- 
commended. 

POWDERY  MILDEW 
Caused  by  Erysiphe  polygomi  D.  C. 

Powdery  mildew  is  serious  on  fall  beans  in  many  of 
the  Southern  States,  and  on  beans  grown  for  the  early 
market.  It  is  characterized  by  white,  mealy  patches 
on  the  surface  of  the  leaves  and  stems.  The  foliage 
soon  turns  yellow  and  dry.  Powdery  mildew  may  be 
controlled  by  dusting  the  plants  with  flowers  of  sul- 


FIG.  47.    BEAN  DISEASES. 

a.  and  b.  Rust  on  leaf  and  pods,  c.  section  through  bean  leaf  showing  bean  rust, 
summer  spores,  d.  section  through  bean  leaf,  showing  bean  rust,  winter  spores,  e. 
anthracnose,  /.  section  through  bean  seed,  showing  relation  of  anthracnose  to  the 
host  (c.  d.  and  /.  after  Whetzel),  g.  Cercospora  leaf  spot,  h.  Isariopsis  griseola  leaf 
spot,  *.  conidiophores  and  conidia  of  Isariopsis. 


Family  Leguminosae  263 

phur,  or  by  spraying  with  potassium  sulphide  at  the 
rate  of  three  ounces  of  the  chemical  dissolved  in  ten 
gallons  of  water. 

SCLEROTINIA   ROT 

Caused  by  Sclerotinia  libertiana  Fckl. 

Sclerotinia  rot  is  a  disease  which  attacks  fall  snap 
beans.  The  trouble  is  prevalent  in  Norfolk,  Virginia, 
where  it  has  been  studied  by  McClintock. x  During 
a  period  of  hot  humid  weather  in  September  the 
disease  may  suddenly  break  out  in  great  severity. 
Usually  withering  and  decaying  of  stems  and  pods 
where  the  plants  are  thickest  is  the  first  symptom  that 
attracts  attention  (fig.  51  c).  On  closely  examining 
infected  stems  and  pods,  we  find  that  they  are  water- 
soaked,  and  overrun  by  the  white  mycelial  growth 
on  which  appear  numerous  hard,  black  sclerotia.  In 
the  field,  the  Black  Valentine  snap  bean  seems  to  be 
more  resistant  to  rot.  For  a  description  of  the 
causative  fungus  and  methods  of  control,  see  lettuce 
drop,  p.  143. 

ANTHRACNOSE 

Caused  by  Colletotrichum  lindemuthianum  (Sacc. 
&  Magn.)  B.  and  C. 

Anthracnose  may  be  considered  one  of  the  most 
destructive    bean    diseases.     However    the    trouble 
1  McClintock,  J.  A.,  Phytopath.    6  :  436-441 ,  19 16. 


264  Diseases  of  Truck  Crops 

depends  on  weather  conditions.  It  is  most  prevalent 
during  periods  of  heavy  night  dews,  or  during  pro- 
longed rains,  and  in  hot  muggy  weather. 

Symptoms.  Anthracnose  is  so  characteristic,  that 
it  cannot  be  mistaken  for  any  other  disease,  except 
perhaps  the  blight.  In  light  attacks,  the  seeds  are 
covered  with  sunken  brown  to  black  specks.  These 
are  especially  evidenced  on  the  black  seeded  varieties. 
In  severe  attacks,  the  seeds  are  covered  with  deep 
sunken  black  spots  which  are  rifted  in  the  center. 
On  the  leaves  the  disease  attacks  the  veins,  which 
become  blackened  and  somewhat  shrunken.  Fre- 
quently it  attacks  the  petioles,  especially  at  the  point 
of  leaf  attachment.  In  this  case  the  foliage  drops  off, 
leaving  the  bare  petioles  or  stems.  Anthracnose  on 
the  leaves  begins  as  small,  circular,  pin-point,  dark  red 
spots  which  enlarge,  and  later  elongate  into  maroon 
colored  pits,  cracks,  or  cankers  (fig.  47  e).  On  young 
seedlings  the  stem  rots  off  a  short  distance  above 
ground. 

The  Organism.  Spores  are  formed  on  the  spots  or 
cankers  on  all  parts  affected  (fig.  47  f).  These  are 
imbedded  in  a  gelatinous  substance  and  can  become 
loosened  only  by  rain  splashing  or  dew.  It  is  at  this 
stage  that  the  disease  becomes  serious,  since  it  is  then 
spread  about  from  plant  to  plant.  When  the  spores 
are  lodged  on  a  new  bean  plant  or  on  a  new  part  of 
the  same  plant,  infection  takes  place  through  the 
penetration  of  the  germ  tube  of  the  germinated 
spores.  It  is  estimated  by  Edgerton1  that  from  one 
1  Edgerton,  C.  A.,  Louisiana  Agr.  Expt.  Sta.  Bui.  119  :  3-55, 1910. 


Family  Leguminosae  265 

half  to^a  million  spores  are  formed  on  one  infected 
pod  alone.  The  period  of  incubation  usually  varies 
from  four  to  six  days. 

In  culture  media,  the  growth  is  at  first  white,  but 
it  soon  becomes  jet  black  in  color.  The  mycelium 
of  the  fungus  is  hyaline,  small  at  first,  but  later  be- 
coming larger  and  darker. 

Control.  Spraying  has  not  given  satisfactory 
results.  The  best  control  is  to  plant  clean  seed  se- 
lected from  clean  pods.  The  latter  before  shelling 
may  be  dipped  for  ten  minutes  in  a  solution  of  one 
part  of  corrosive  sublimate  to  a  thousand  of  water. 
The  treated  pods  are  then  dried  in  the  sun,  shelled, 
and  the  seed  put  away  in  dry  mason  jars  until  the 
following  spring.  Should  weevils  threaten  these 
seeds,  they  may  be  fumigated  with  carbon  bisulphide. 
By  reserving  a  plot  destined  for  bean  seed,  by  care- 
fully destroying  infected  plants,  and  by  selecting 
clean  pods  and  seed,  anthracnose  and  blight  may  be 
kept  in  check. 

Under  no  circumstances  should  an  infected  field  be 
cultivated  in  damp  weather,  or  when  the  dew  is  still 
on  the  plants.  When  this  is  done  the  spores  of  the 
fungus  are  scattered  broadcast  in  the  field.  As 
for  resistant  varieties,  there  is  very  little  to  select 
from.  However,  Barrus1  found  that  the  Wells 
red  kidney  bean  is  most  resistant  to  anthracnose.  It 
is  therefore  recommended  for  trial  in  localities  where 
anthracnose  prevails.  In  selecting  for  seed  resistant 
varieties,  these  must  of  course  be  artificially  inoculated 

x  Barrus,  M.  F.,  Phytopath.  5  : 303-311,  1915. 


266  Diseases  of  Truck  Crops 

with  spores  of  the  fungus.  This  will  make  sure  that 
the  parasite  has  been  placed  on  the  host.  If  there 
is  any  difference  in  resistance,  it  will  be  evidenced  by 
the  amount  of  infection  developing  on  each  variety 
tested.  In  this  connection  it  should  be  remembered 
that  there  are  numerous  strains  of  C.  lindemuihianum, 
some  of  which  are  very  virulent  while  others  are  less 
so.  In  inoculating  for  resistant  varieties,  an  attempt 
should  be  made  to  secure  pure  culture  strains  from 
various  localities. 

STEM  ANTHRACNOSE 
Caused  by  Colletotrichum  caulicolum  H.  and  W. 

A  serious  stem  rot  attacks  the  Kentucky  Wonder 
bean.  The  disease  differs  from  anthracnose  described 
above  in  that  the  former  destroys  the  stems  of  the 
plant.  Observations  made  by  Heald  and  Wolf1 
show  that  the  disease  girdles  the  stem,  and  also 
causes  deep  fissured  cankers  on  one  side  of  it.  The 
trouble  has  been  found  in  only  one  locality  in  Texas, 
and  it  is  doubtful  if  it  is  prevalent  elsewhere.  Little 
is  known  of  the  control  of  this  disease. 

ANGULAR  LEAF  SPOT  (fig.  47  g),  see  COWPEA,  p.  271. 

SOUTHERN  BLIGHT,  see  PEPPER,  p.  305. 

ROOT  ROT  (fig.  49  a),  see  RHIZOCTONIA,  p.  45. 

TEXAS  ROOT,  see  SWEET  POTATO,  p.  175. 

ROOT  KNOT,  see  NEMATODE,  p.  49. 

1  Heald,  F.  D.,  and  Wolf,  F.  A.,  U.  S.  Dept.  of  Agr.  Bur.  PI.  Ind. 
Bui.  226  :  35-36,  1912. 


FIG.  48.     DISEASES  OF  LIMA  BEAN. 

a.  b.  c.  different  stages  of  downy  mildew  on  pods,  d.  tuft  of  conidiophores  and 
conidia  of  Phythophthora  phaseoli,  e.  same  as  d.  but  greatly  enlarged,  /.  g.  conidia 
germinating  by  means  of  a  germ  tube,  h.  i.  j.  k.  germination  of  conidia  by  means  of 
zoospores,  I.  germinating  zoospores  (d.  to  /.  after  Thaxter),  m.  n.  fertilization  of  the 
oogonium  by  the  antheridium,  o.  Phoma  blight  on  foliage,  p.  Phoma  blight  on  pods 
(o.  and  p.  after  Halsted),  r.  mature  oospores  of  P.  phaseoli  (a.  to  c.,  m.  n.  and  r. 
after  Clinton). 


Family  Leguminosae  267 

DISEASES  OF  THE  LIMA  BEAN  (Phaseolus 

lunatus  var.  macrocarpus) 

Lima  beans,  whether  climbing  or  dwarf,  are  usually 
considered  hardy.  This  is  generally  true  under 
favorable  weather  conditions.  But  in  hot  moist 
weather,  truckers  may  lose  heavily  from  various 
diseases. 

BLIGHT,  see  BEAN,  p.  260. 

DOWNY  MILDEW 
Caused  by  Phytophtora  phaseoli  Thax. 

Perhaps  the  greatest  damage  in  wet  seasons  to 
lima  bean  culture  of  both  the  pole  and  the  dwarf 
varieties  is  downy  mildew.  The  damage  from  this 
disease  equals  that  from  the  anthracnose  on  snap  and 
other  varieties  of  Phaseolus  vulgaris. 

Symptoms.  It  is  most  conspicuous  on  the  pods, 
where  it  forms  a  dense,  dirty  white  mycelial  growth 
(fig.  48  a-c).  The  trouble  appears  first  on  one  side 
of  the  pod,  and  then  works  its  way  through  to  the 
other  side.  Infected  pods  wilt,  shrink,  and  eventually 
dry  up  and  die.  In  early  cases  of  infection,  the  dis- 
eased area  is  separated  from  the  healthy  by  a  purplish 
border.  Occasionally  the  blossoms  are  affected,  in 
which  case  they  wither  and  drop  off.  On  the  leaves 
the  disease  is  manifested  as  irregular  purplish  dis- 
coloration, especially  on  the  veins,  but  there  seems 
to  be  no  evidence  of  the  fungus  growth  on  it . 


268  Diseases  of  Truck  Crops 

The  Organism.  The  mycelium  is  hyaline,  non-sep- 
tate, and  in  other  respects  not  different  from  other 
downy  mildews.  The  conidiophores  are  long  and 
little  branched  (fig.  48  d,  e),  the  conidia  are  hyaline, 
elliptical  to  ovoid  in  shape,  germinating  by  means  of 
motile  zoospores  (fig.  48  f-1).  The  oospores  or  sexual 
resting  spores  are  formed  in  the  same  way  as  in 
Pythium  (fig.  48  m,  n,  r),  see  p.  43. 

Control.  Downy  mildew  is  carried  over  in  the  seed 
as  dormant  mycelium.  Hence  all  shriveled  seed 
should  be  discarded.  In  badly  infected  fields,  crop 
rotation  should  be  resorted  to.  The  burning  of  trash 
and  old  bean  plants  is  also  advised.  Finally  three 
sprayings  with  4-4-50  Bordeaux  mixture  during  the 
growing  season  will  keep  the  disease  well  in  check. 

RUST,  see  BEAN,  p.  262. 

POWDERY  MILDEW,  see  BEAN,  p.  262. 

POD  BLIGHT 
Caused  by  Phoma  subcircinata  E.  and  E. 

As  the  name  indicates,  the  disease  chiefly  attacks 
the  pods.  Blight  is  indicated  on  them  by  the  appear- 
ance of  large  brown  patches  (fig.  48  o,  p).  The 
pycnidia  of  the  fungus  are  arranged  in  concentric 
zones.  In  severe  cases,  the  disease  works  from  the 
pods  to  the  seed,  considerably  reducing  the  yield. 
On  the  leaves  the  symptoms  are  the  same  as  on  the 
pods.  Spraying  with  Bordeaux  will  control  the 
trouble. 


FIG.  49.     BEAN  DISEASES. 

a.  Rhizoctonia  root  rot,  b.  root  knot  on  lima  beans. 


Family  Leguminosae  269 

LEAF  BLOTCH 
Caused  by  Cercospora  canescens  E.  and  M/ 

This  disease,  so  far  as  is  known,  is  not  generally 
distributed.  It  is  found  in  certain  trucking  centers 
in  Texas.  On  the  leaves  the  spots  are  circular,  but 
somewhat  angular.  The  center  of  the  spots  is  gray 
with  a  reddish  brown  border,  the  outside  of  which 
divides  the  diseased  from  the  healthy  tissue.  The 
conidiophores  are  equally  abundant  on  both  surfaces, 
the  spores  are  hyaline,  straight  or  curved,  slender  and 
one  to  many  septate.  While  no  experiments  have 
been  made  on  the  disease,  spraying  with  Bordeaux 
is  recommended. 

LEAF  SPOT 
Caused  by  Isariopsis  griseola  Sacc. 

The  disease  is  confined  to  the  foliage  only.  The 
spots  produced  are  small  and  angular  with  no 
colored  borders  (fig.  47  h,  i).  On  the  under  side 
of  the  leaf,  the  fungus  forms  a  gray  moldy  growth 
on  the  spot,  where  large  numbers  of  the  spores 
are  produced.  The  disease  is  not  widely  dis- 
tributed, and  may  be  controlled  by  spraying  with 
Bordeaux. 

ROOT  ROT,  see  RHIZOCTONIA,  p.  45. 

TEXAS  ROOT  ROT,  see  SWEET  POTATO,  p.  175. 

ROOT  KNOT  (fig.  49  b),  see  NEMATODE,  p.  49. 


270          Diseases  of  Truck  Crops 

DISEASES  OP  THE  COWPEA~(Vigna  sinensis) 

In  the  South,  the  cowpea  is  extensively  grown  as  a 
truck  crop.  It  is  cultivated  for  its  edible  green  pods, 
and  dried  peas,  and  often  takes  the  place  of  the  bean. 

STREAK 
Caused  by  Bacillus  lathyri  Manns  and  Taub. 

Streak  is  a  serious  disease  which  until  now  has 
usually  been  mistaken  for  other  troubles .  The  disease 
is  the  same  as  streak  on  the  sweet  pea  and  clovers. 

Symptoms.  Like  the  bacteriosis  of  the  bean,  streak 
makes  its  appearance  in  a  season  of  heavy  dew.  On 
the  cowpea  it  usually  appears  just  as  the  plant  begins 
to  bloom.  It  is  manifested  along  the  stems  by  light 
reddish  brown  to  dark  brown  spots  and  streaks,  the 
older  of  which  are  almost  purple,  having  their  origin 
usually  near  the  ground.  This  indicates  distribution 
by  spattering  rain  and  infection  through  the  stomata 
or  through  insect  injury.  The  disease  becomes 
distributed  quickly  over  the  mature  stems  until  the 
cambium  and  deeper  tissues  are  destroyed  in  con- 
tinuous areas,  and  the  plant  dies  prematurely.  From 
the  stem  the  disease  spreads  to  the  petioles,  peduncles, 
and  pods,  the  symptoms  in  these  cases  being  similar 
to  those  on  the  stems.  On  the  leaves,  however,  the 
disease  appears  as  small  circular  spots,  which  grad- 
ually coalesce  and  eventually  involve  the  entire  leaf. 
When  killed,  the  leaf  presents  a  dark  brownish  ap- 
pearance. 


Family  Leguminosae  271 

The  Organism.  Bacillus  lathy ri  as  worked  out  by 
Manns, x  is  rod-shaped,  occurring  singly,  never  found 
in  chains,  and  seldom  united  by  twos  or  fours, 
motile  by  means  of  flagella.  It  produces  no  spores, 
no  capsules,  no  zooglea,  liquefies  gelatin  completely 
in  about  three  weeks,  and  produces  no  gas. 

Control.  Rotation  of  crops  is  helpful;  but  since 
streak  attacks  numerous  leguminous  crops,  such  as 
bean  and  clovers,  these  should  be  excluded.  Other 
methods  of  control  are  as  yet  unknown. 

RUST,  see  BEAN,  p.  262. 

POWDERY  MILDEW,  see  BEAN,  p.  262. 

ANGULAR  LEAF  SPOT 

Caused  by  Cercospora  cruenta  Sacc.;  Cercospora 
dolichi  E.  and  E. 

Angular  leaf  spot  is  a  common  disease  on  cowpeas. 
When  it  attacks  the  leaves,  they  are  covered  with 
angularrrusty  red  spots,  the  leaves  turn  yellow  and 
drop  prematurely.  On  the  stems  the  spots  are  ir- 
regular, elongated,  dark  colored,  slightly  sunken, 
and  later  forming  cankers.  The  latter  often  crack 
and  expose  the  stems  to  the  attacks  of  various  other 
parasitic  and  even  saprophytic  fungi.  Under  favor- 
able conditions  of  moisture,  the  spots  on  the  leaves 
or  stems  are  covered  with  a  brownish  downy  growth 
made  up  of  the  conidiophores  and  conidia.  No 
methods  of  control  are  known. 

«  Manns,  T.  P.,  Delaware  Agr.  Expt.  Sta.  Bui.  108  : 3-44, 1915. 


272  Diseases  of  Truck  Crops 

WILT,  YELLOWS 
Caused  by  Fusarium  tracheiphila  Ew.  Sm. 

In  the  light  sandy  to  loamy  soils,  wilt  is  the  greatest 
drawback  to  pea  culture.  The  disease  is  most  pre- 
valent in  the  Southern  States. 

Symptoms.  It  does  not  seem  to  attack  young 
seedlings,  but  appears  only  when  the  plant  is  about 
six  weeks  old  and  upwards.  In  the  field,  scattered 
plants  turn  yellow  and  begin  to  drop  their  leaves,  the 
stems  become  bare  (fig.  50  a),  and  the  plants  finally 
die.  On  pulling  out  a  diseased  plant,  the  main  root 
will  apparently  be  sound,  but  the  lateral  rootlets 
will  be  dead,  marking  the  seat  of  infection.  A 
more  definite  symptom  of  wilt  is  a  browning  of 
the  interior  fibrovascular  bundles  of  roots,  stems, 
and  petioles.  This  may  be  readily  ascertained  by 
splitting  open  lengthwise  a  root  or  stem  of  a  sus- 
pected plant. 

The  Organism.  From  unpublished  work  by  the 
author,  it  is  definitely  proven  that  F.  tracheiphila  is 
distinct  from  Fusarium  wilts  of  the  cotton,  okra, 
and  watermelon.  The  Fusarium  wilt  of  the  cowpea 
is  caused  by  F.  tracheiphila,  which  produces  only  the 
conidial  stage  and  has  no  relationship  whatsoever 
with  Necosmospora,  or  any  other  ascospore  stage. 
The  cowpea  Fusarium  may  be  found  in  fields  which 
are  also  infected  with  okra  Fusarium.  In  this  case, 
the  field  is  infected  with  two  distinct  organisms,  thus 
making  it  sick  to  both  cowpeas  and  okra.  The  cow- 


FIG.  50.     DISEASES  OF  THE  Cow  PEA. 

a.  Fusarium  wilt,  b.  field  of  cow  peas  killed  by  Texas  root  rot,  c.  root  knot,  d. 
row  of  iron  cow  pea  resistant  to  Fusarium  wilt  in  sick  field  where  other  varieties  of 
peas  have  died  (a.  and  d.  after  W.  A.  Orton). 


Family  Lcguminosae  273 

pea  Fusarium  is  parasitic  only  on  the  cowpea,  and 
so  far  as  is  known  does  not  attack  any  of  the  other 
cultivated  legumes. 

Control.  Diseased  fields  may  be  sown  with  beans 
or  any  other  legume  except  cowpeas.  Crops  other 
than  legumes  may  also  be  grown  there.  The  develop- 
ment of  resistant  varieties  is  also  a  promising  method 
of  control.  Orton1  has  already  developed  the  Iron 
cowpea  (fig.  50  d),  a  variety  which  is  resistant  to  wilt 
and  partly  also  to  Nematode. 

ROOT  ROT,  see  RHIZOCTONIA,  p.  45. 

TEXAS  ROOT  ROT  (fig.  50  b),  see  OKRA,  p.  175. 

ROOT  KNOT  (fig.  50  c),  see  NEMATODE,  p.  49. 

DISEASES  OF  THE  GARDEN  PEA  (Pisum 
sativum) 

Like  the  bean  and  cowpea,  the  garden  pea  is  sub- 
ject to  numerous  diseases,  some  of  which  are  of  great 
economic  importance.  However  many  of  these  dis- 
eases may  be  controlled. 

STEM  BLIGHT 
Caused  by  Pseudomonas  pisi  Sack. 

Blight  is  a  new  disease  recently  found  by  Sackett2 
in  the  pea  fields  of  Colorado.  So  far  as  is  known,  the 

1  Orton,  W.  A.,  U.  S.  Dept.  of  Agr.  Bur.  PI.  Ind.  Bui.  17  : 9-36, 
1902. 

2  Sackett,  W.  G.,  Colorado  Agr.  Expt.  Sta.  Bui.  218  : 3-43, 1916. 

18 


274    Diseases  of  Truck  Crops 

trouble  does  not  seem  to  occur  in  the  other  States 
where  peas  are  extensively  grown.  In  Colorado, 
blight  has  suddenly  made  its  appearance  on  a  pea 
area  of  500,000  acres,  seriously  threatening  the  pro- 
fitable growing  of  the  crop. 

Symptoms.  On  the  stems  and  leaves  (fig.  51  b) 
the  disease  may  be  recognized  by  watery  olive  green 
to  drab  brown  spots  and  by  yellowish  watery  bruises 
on  the  leaflets  and  stipules.  The  roots  seem  to  be 
free  from  the  attacks  of  blight.  Infection  seems  to 
start  on  the  stem,  near  the  ground  level,  and  from 
there  to  work  upwards.  Lower  leaves  are  usually 
the  first  to  die.  Occasionally  the  infected  plants 
send  out  new  shoots  below  the  infected  area.  The 
new  growth  is  sometimes  unmolested  but  ordinarily 
it  too  becomes  blighted. 

The  Organism.  Pseudomonas  pisi  is  a  short 
rod,  rounded  at  both  ends,  and  motile  by  means 
of  polar  flagella.  It  produces  no  spores,  no  cap- 
sules, and  no  zooglea  and  no  involution  forms. 
It  produces  no  gas,  and  can  stand  drying  of  thirteen 
days. 

Control.  Certain  varieties  seem  to  be  more  re- 
sistant than  others.  The  development  of  resistant 
varieties  is  recommended.  All  trash  and  diseased 
materials  should  be  destroyed  by  fire  and  -not  fed  to 
animals.  It  is  not  known  if  spraying  will  control 
this  disease.  In  badly  affected  fields,  spraying  with 
Bordeaux  may  be  tried. 

DAMPING  OFF,  see  PYTHIUM,  p.  43. 

RUST,  see  BEAN,  p.  262. 


FIG.  51.     DISEASES  OF  THE  GARDEN  PEA  AND  BEAN. 

a.  Thielavia  root  rot,  to  the  right  diseased  plant  with  no  root  system,  to  the  left 
healthy,  b.  stomatal  leaf  infection  by  Pseudomonas  pisi,  c.  Sclerotinia  libertiana 
rot  on  bean  pods,  d.  endospore  of  Thielavia  basicola,  e.  chlamydospores  of  T.  basicola. 


Family  Leguminosae  275 

THIELAVIA  ROOT  ROT 
Caused  by  Thielavia  basicola  Zopf . 

Root  rot  is  a  common  disease  in  fields  devoted  to 
peas  for  a  period  of  years.  The  trouble  on  the  garden 
and  field  pea  is  identical  with  that  on  the  sweet  pea. 

Symptoms.  Plants  severely  infected  with  Thie- 
lavia have  practically  no  root  system,  since  this  is 
destroyed  by  the  fungus  as  rapidly  as  formed  (fig. 
51  a).  All  that  is  left  of  the  root  system  is  a  charred 
blackened  stub.  The  diseased  host  constantly  at- 
tempts to  produce  new  roots  above  the  injured  part 
but  these  in  turn  also  become  infected.  Such  plants 
linger  for  a  long  time,  but  fail  to  set  pods  which  are 
of  any  value. 

The  Organism.  The  mycelium  of  Thielavia  basicola 
is  hyaline,  septate,  and  branched.  The  mycelium 
becomes  somewhat  grayish  with  age.  Three  kinds  of 
spore  forms  are  produced — endospores  (fig.  51  d), 
chlamydospores  (fig.  51  e),  and  ascospores.  Endo- 
spores are  so  called  because  they  are  formed  inside 
a  special  thread  of  the  mycelium.  This  is  the  spore 
form  that  commonly  occurs  in  pure  cultures  of  arti- 
ficial media  and  on  the  host.  The  endospore  case  is 
formed  on  terminal  branches  with  a  somewhat 
swollen  base  and  a  long  tapering  cell.  The  endo- 
spores are  formed  in  the  apex  of  this  terminal  cell  and 
are  pushed  out  of  the  ruptured  end  by  the  growth  of 
the  unfragmented  protoplasm  of  the  base.  They  are 
hyaline,  thin  walled,  and  oblong  to  linear  in  shape. 


276          Diseases  of  Truck  Crops 

The  chlamydospores  are  thick  walled,  dark  brown 
bodies  borne  on  the  same  mycelium  as  the  endospores. 
This  type  of  spore  is  formed  in  great  abundance  on 
the  host  and  particularly  within  the  affected  tissue. 
The  ascospores  are  lenticular  in  shape  and  are  borne 
in  asci  or  sacs  within  black  perithecia.  This  stage 
however  has  not  been  found  on  the  pea  or  in  pure  cul- 
ture. 

Control.  Thielavia  basicola  is  a  soil-inhabiting 
fungus.  With  infected  pea  fields,  soil  sterilization  is 
of  course  out  of  the  question.  The  method  of  control 
suggested  is  crop  rotation.  Investigations  by  John- 
son1 have  shown  that  the  following  vegetable  crops 
are  not  subject  to  Thielavia  root  rot:  potato,  sweet 
corn,  sweet  potato,  cabbage,  onion,  parsnip,  carrot, 
beet,  eggplant,  and  peppers.  These  crops  may  there- 
fore be  safely  used  in  a  crop  rotation,  the  system  of 
which  is  best  worked  out  by  the  trucker  himself. 

POWDERY  MILDEW,  see  BEAN,  p.  262. 

POD  SPOT 

Caused  by  Spharella  pinodes  (Berk,  and  Bl.)  Niessl. 

Pod  spot  is  a  disease  which  is  of  even  greater  eco- 
nomic importance  than  Thielavia  root  rot.  The 
disease  does  not  confine  itself  to  the  pods  alone,  but 
also  involves  the  leaves  and  stems.  The  trouble 
however  is  known  by  truckers  as  pod  spot. 

1  Johnson,  J.f  U.  S.  Dept.  of  Agr.  Jour.  Agr.  Research,  7  : 261-300, 
1916. 


Family  Leguminosae  277 

Symptoms.  On  the  stem  the  trouble  appears  as 
numerous  elongated  lesions.  These  spread  to  such 
an  extent  as  actually  to  girdle  the  affected  stem.  On 
the  leaves  are  formed  oval  spots,  grayish  in  the  center, 
and  limited  by  a  dark  band.  The  pods  too  become 
badly  attacked  and  the  symptoms  there  resemble 
those  on  the  stems.  The  disease  works  its  way  from 
ihe  pods  to  the  seed  within. 

The  Organism.  The  causative  fungus  has  two 
spore  stages.  The  pycnidia  bear  the  hyaline,  two 
celled  spores  and  are  formed  within  the  dead  tissue  of 
the  affected  stems,  leaves,  or  pods.  The  pycnidial 
stage  is  known  as  Ascochyta  pisi  Lib.  The  winter  or 
ascospore  stage  has  only  recently  been  discovered 
by  Stone,  *  who  found  it  on  pods  and  stems  previously 
affected,  and  on  culture  media.  The  fungus  may  be 
carried  from  year  to  year  as  dormant  mycelium  within 
the  seed,  or  in  the  ascospore  stage. 

Control.  Seed  treatment  will  not  be  of  any  value 
since  the  fungus  is  hidden  within  the  seed.  No  out- 
side treatment  is  capable  of  reaching  the  parasite 
within.  Seed  should  be  secured  from  localities 
known  to  be  free  from  the  disease.  Rotation  of 
crops  is  also  recommended.  Giving  the  field  a 
rest  from  peas  or  hairy  vetch  for  at  least  three 
years  is  recommended.  In  badly  affected  local- 
ities, susceptible  varieties,  such  as  French  June, 
Market  Garden,  American  Wonder,  should  be  dis- 
carded. The  Alaska  variety  is  claimed  to  be  more 
resistant. 

1  Stone,  R.  E.,  Annales  Mycol.,  10  :  564-592, 1912. 


278  Diseases  of  Truck  Crops 

SEPTORIA  LEAF  SPOT 
Caused  by  Septoria  pisi  Westd. 

The  disease  greatly  resembles  pod  spot.  But  a 
microscopical  examination  of  the  fruit  of  the  two  will 
reveal  the  difference.  Septoria  leaf  spot  is  of  little 
economic  importance. 

ROOT  ROT,  see  RHIZOCTONIA,  p.  45. 

ROOT  KNOT,  see  NEMATODE,  p.  49. 

WEEDS 

Of  the  numerous  legume  weeds,  few  if  any  are 
troublesome  in  trucking.  None  are  likely  to  be 
carriers  of  the  diseases  which  attack  beans  and  peas. 


CHAPTER  XVIII 

FAMILY  LILIACE^E 

THIS  family  is  an  important  one,  since  it  furnishes 
such  crops  as  asparagus,  chive,  garlic,  leek,  onion, 
and  shallot.  According  to  the  Thirteenth  Census 
of  the  United  States,  the  total  1909  American  area 
devoted  to  asparagus  was  estimated  at  25,639  acres 
and  the  crop  valued  at  $2,246,631.  The  States 
ranked  according  to  largest  area  devoted  to  aspara- 
gus are  as  follows:  California,  New  Jersey,  Illinois, 
South  Carolina,  Pennsylvania,  and  New  York. 
States  with  less  than  1,000  acres  are  here  omitted. 
The  total  area  in  the  United  States  devoted  to 
onions  in  1909,  including  chive,  garlic,  leek,  and 
shallot,  of  which  there  are  no  records,  was  estimated 
at  47,625  acres,  and  the  total  crop  valued  at  $6,709,- 
047.  The  States  ranked  according  to  acreage  in 
onions  were  as  follows :  Ohio,  New  York,  Texas,  Cali- 
fornia, Illinois,  Indiana,  Louisiana,  Massachusetts, 
Kentucky,  New  Jersey,  Michigan,  and  Minnesota. 
States  with  less  than  one  thousand  acres  are  omitted. 

DISEASES  OF  THE  ASPARAGUS  (Asparagus 

officinalis) 

Asparagus  may  be  considered  a  hardy  host  when 
grown  under  proper  cultural  and  climatic  conditions. 

279 


28o  Diseases  of  Truck  Crops 

Where  this  is  not  the  case  it  soon  becomes  subject  to 
a  few,  but  serious,  diseases. 

LEOPARD  SPOT 

Cause,  Unknown. 

The  disease,  as  the  name  indicates,  consists  of  large 
irregular  ashen  colored  spots,  each  surrounded  by  a 
dark  border.  No  treatment  which  keeps  the  disease 
in  check  is  known. 

RUST 
Caused  by  Puccinia  asparagi  D.  C. 

Asparagus  rust  does  not  seem  to  be  limited  in  its 
geographic  distribution,  as  it  has  been  found  in  all 
States  where  the  crop  is  grown.  It  is  especially  se- 
rious in  California,  New  Jersey,  and  all  the  other  im- 
portant asparagus  regions. 

Symptoms.  Rust  does  not  attack  the  asparagus 
tips  which  are  cut  for  the  market.  It  attacks  the 
green  tops  which  develop  after  cutting  has  ceased. 
Affected  tops  redden,  and  these  when  carefully  ex- 
amined will  reveal  reddish  rusty  pimples  or  sori  on 
the  stems  (fig.  52  a)  and  needles.  In  severe  infection, 
the  reddened  tops  become  bright  yellow,  the  needles 
fall  off  prematurely,  exposing  a  bare  dead  stalk  cov- 
ered with  numerous  rust  sori.  The  symptom  is 
generally  found  in  September  and  the  pimples  are 


FIG.  52.    ASPARAGUS  DISEASES. 

a.  Asparagus  rust  on  stems,  showing  sori  with  winter  spores,  b.  cluster  cup  stage 
of  Puccinia  asparagi,  c.  Uredo  or  summer  spores  of  P.  asparagi,  d.  Teleuto  or  winter 
spores  of  P.  asparagi  (b.  to  d.  after  R.  E.  Smith). 


Family  Liliaceae  281 

made  up  of  the  teleuto  or  winter  spores  of  the  fungus. 
In  old  asparagus  fields,  rust  may  appear  early  in  the 
season.  In  this  case  instead  of  rusty  brown  son 
there  appear  on  the  main  stems  and  branches,  but 
not  on  the  needles,  numerous  bright  cup-shaped 
bodies,  containing  the  aecidial  or  spring  spores. 
This  form  occurs  about  May  but  disappears  in  June 
or  July.  This  stage  is  immediately  followed  by  red 
pustules  which  contain  the  uredo  or  summer  spores. 
Later  in  August  and  September,  and  as  already 
stated  the  teleutospores  appear.  The  latter  help 
to  carry  the  fungus  over  winter  and  unfavorable 
conditions.  The  effect  of  asparagus  rust  is  an  in- 
direct weakening  of  the  crowns  of  the  plant.  Affected 
tips  fail  to  store  up  the  necessary  starches  and  sugars 
for  the  underground  crowns.  The  latter  being  un- 
der-fed become  weak,  soft,  and  subject  to  the  attacks 
of  various,  soil-inhabiting  parasites. 

The  Organism.  The  life  history  of  Puccinia  as- 
paragi  has  been  carefully  worked  out  by  Smith x  and 
others.  The  mycelium  of  the  fungus  is  long  and 
narrow,  extensively  branched,  deriving  its  food  by 
means  of  suckers  or  haustoria  which  penetrate  the 
cells  of  the  host.  The  aecidiospores  are  formed  in 
chains,  coming  up  from  the  mass  of  mycelium  at  the 
base  of  the  cup  (fig.  52  b).  The  uredospores  (fig. 
52  c)  are  dark  in  color  and  are  borne  singly  in  the 
uredo  pustules.  Both  the  aecidio-  and  uredospores 
are  one  celled,  and  both  germinate  by  means  of  a  germ 
tube  which  penetrates  the  host.  The  black  rust  or 

1  Smith,  R.  E.,  California  Agr.  Expt.  Sta.  Bui.  165  :  5-99,  1905. 


282  Diseases  of  Truck  Crops 

teleutospores  (fig.  52  d)  are  two  celled,  thick  walled, 
dark  colored,  and  borne  singly  on  long  stalks.  The 
teleutospores  must  first  winter  over  before  they  can 
germinate.  In  germination  each  cell  sends  out  a 
thick  short  germ  tube  which  divides  at  the  tip  into 
four  parts,  each  of  which  produces  a  side  branch 
which  bears  secondary  spores  known  as  sporidia. 
The  latter  break  away,  and  when  falling  on  a  fresh 
green  asparagus  top  germinate  by  sending  out  a  germ 
tube  which  penetrates  the  host.  After  proper  incu- 
bation, the  cluster  cup  stage  appears,  and  the  same 
life  cycle  is  repeated  over  again. 

Control.  Asparagus  rust  may  be  kept  in  check  by 
taking  advantage  of  certain  cultural  conditions. 
Rust  is  more  abundant  in  seasons  with  insufficient 
rainfall  or  on  lands  which  dry  out  rapidly,  while 
soils  which  have  an  abundance  of  moisture  harbor 
little  or  no  rust.  In  moist  soils,  asparagus  plants  are 
more  vigorous  than  those  grown  under  dry  conditions 
and  vigorous  plants  are  less  subject  to  rust  than  weak 
ones.  Irrigation,  therefore,  wherever  possible  will 
help  to  keep  the  rust  in  check.  Rust  infection  can 
never  take  place  unless  there  is  plenty  of  dew  to 
enable  the  spores  of  the  fungus  to  germinate.  In 
low  lying  places,  dew  formation  is  heavier  and  hangs 
on  longer  than  in  more  elevated  regions.  As  far  as 
possible,  asparagus  should  be  grown  on  high,  well 
exposed  moist  lands.  In  regions  subject  to  rains  and 
heavy  dews,  spraying  is  recommended.  Sirrine1  has 

1  Sirrine,  F.  A..  N.  Y.  (Geneva)  Agr.  Expt.  Sta.  Bui.  188  :  122- 
166,  1 900. 


Family  Liliaceae  283 

obtained  good  results  by  spraying  with  5-5-40  Bor- 
deaux to  which  was  added  2  gallons  of  a  resin 
mixture  (made  up  of  5  Ibs.  resin,  I  Ib.  potash,  or  lye, 
I  pint  fish  oil,  and  5  gals,  water)  to  each  10  gallons  of 
Bordeaux.  Another  good  treatment  is  dusting  the 
asparagus  tops  with  flowers  of  sulphur.  To  be 
effective,  this  must  be  applied  in  the  form  of  a  fine 
smoke-like  dust.  If  the  tops  are  too  dry  they  may  be 
wetted  with  whale  oil  soap  water,  or  the  grower  must 
wait  for  a  heavy  dew  or  rain.  There  are  many  ' '  dust 
sprayers"  on  the  market,  many  of  which  have  their 
good  qualities.  There  are  two  main  types  of  dust 
sprayers,  the  "seed  sower "  and  the  "fan  blower.'* 
The  former  throws  a  tremendous  dust  cloud.  The 
fan  blower  sends  out  small  clouds  and  covers  less 
area.  The  number  of  applications  will  depend  on  the 
amount  of  dew  in  the  season.  In  general,  three 
applications  using  one  half  a  sack  of  flowers  of  sul- 
phur per  acre  during  the  season  will  suffice.  The 
practice  of  applying  ordinary  salt  (NaCl)  to  the  soil 
will  not  injure  the  asparagus  crop  but  it  will  fail  to 
control  rust. 

Resistant  Varieties.  It  is  a  well-known  fact  that 
some  varieties  of  asparagus  are  more  resistant  to  rust 
than  others.  The  Canovers  Colossal  which  is  the 
canning  type  is  a  variety  which  is  badly  subject  to 
rust.  The  same  is  also  true  for  the  Columbian 
White  and  the  Moore's  Cross-Bred  variety.  On 
the  other  hand  the  Palmetto  Type  and  the  French 
or  Argenteuil  Barrs  mammoth  are  fairly  resistant. 

Natural  Enemies.     Puccinia   asparagi,    although 


284    Diseases  of  Truck  Crops 

itself  a  parasite,  is  in  turn  parasitized  by  three  other 
fungi. 

1.  Darluca  filum  Cast.     This  fungus  develops  on 
the  rust  pustules,  living  directly  on  the  mycelium 
and  spores  of  its  host. 

2.  Tubercularia  persicina  Dilt.     This  fungus  is 
not  as  common  as  the  first  one. 

3.  Cladosporium  sp.     This  is  a  common  fungus 
which  is  often  abundantly  found  on  rust  pustules. 
All  or  any  of  these  three  natural  enemies  may  be 
readily  grown  in  pure  culture  and   spread  about 
broadcast  wherever  the  rust  is  abundant  and  of 
economic  importance. 

DAMPING  OFF,  see  RHIZOCTONIA,  p.  45. 

DISEASES  OF  THE  CHIVE  (Allium  schoenopo- 
rasum) 

RUST 

Caused  by  Pucdnia  porri  (Sow.)  Wint. 

This  rust,  though  prevalent  in  Europe,  has  been 
reported  but  once  in  the  United  States  by  Clinton1 
as  attacking  also  onions.  It  is  characterized  by  a  yel- 
lowing of  the  leaves  which  die  prematurely.  On  care- 
fully examining  the  infected  leaves  we  find  the  uredo 
pustules,  which  are  minute,  reddish,  and  covered  with 
a  reddish  powder.  The  teleuto  pustules  are  black  and 

1  Clinton,  G.  P.,  Connecticut  Agr.  Expt.  Sta.  Rpts.  1909-1910  : 
726. 


FIG.  53.     ONION  DISEASES. 

a.  Bacterial  rot  (after  Stewart),  b.  Botrytis  rot,  c.  healthy,  d.  Sclerotium  rot,  e. 
onion  storage  house,  /.  type  of  commercial  storage  houses,  p..  interior  of  storage 
house,  showing  method  of  stacking  crates  (/.  and  g.  after  W.  R.  Beattie). 


Family  Liliaceae  285 

covered  by  the  host  epidermis.     Chive  rust  is  dis- 
tinct from  the  onion  rust. 

DISEASES  OF  THE  ONION  (Allium  cepa) 

The  onion  is  commonly  attacked  by  numerous  dis- 
eases. Fortunately  most  of  them  may  be  controlled, 
by  proper  care,  and  timely  preventive  methods. 

SOFT  ROT 

Caused  by  Bacillus  caratovorus  Jones. 

The  disease  was  first  studied  by  Stewart,  *  who  how- 
ever did  not  determine  the  causative  organism,  but 
merely  referred  it  to  a  species  of  Bacillus.  The  writer, 
however,  was  able  to  prove  that  soft  rot  of  onions  is 
caused  by  the  same  organism  which  causes  a  similar 
rot  on  carrots  and  other  vegetables. 

The  rot  on  the  onion  often  starts  at  the  neck  of  the 
bulb  which  is  spoken  of  as  "  weak  in  the  neck. ' '  Sound 
bulbs  are  hard  at  the  neck,  but  when  rot  sets  in,  the 
outer  layer  remains  sound  while  the  interior  tissue 
soft  rots  (fig.  53  a) .  Sometimes  a  single  scale  is  found 
rotted  within  the  bulb,  and  the  others  apparently 
remain  healthy.  At  other  times  a  sound  scale  may 
be  found  between  two  rotted  ones.  Occasionally 
the  rot  is  confined  to  the  outer  fleshy  scale,  in  which 
case  it  is  spoken  of  as  "slippery  onion. "  In  storage, 

1  Stewart,  F.  C.,  New  York  (Geneva)  Agr.  Expt.  Sta.  Bui.  164: 
209-212,  1899. 


286  Diseases  of  Truck  Crops 

under  proper  conditions  of  ventilation  and  tempera- 
ture, the  rot  progresses  very  slowly.     However,  in 
poorly  constructed  houses  the  bulbs  rot  very  fast  and 
the  disease  then  spreads  by  contact. 
DAMPING  OFF,  see  PYTHIUM,  p.  43. 

BLIGHT,  DOWNY  MILDEW 
Caused  by  Peronospora  schleideni,  Ung. 

Of  all  the  onion  diseases,  blight  (also  known  as 
downy  mildew)  is  perhaps  the  most  important  from 
an  economic  standpoint.  It  may  often  wipe  out 
from  seventy  per  cent,  of  the  stand  to  the  en  tire  crop. 
The  disease  usually  accompanies  muggy,  damp,  or 
rainy  weather. 

Symptoms.  The  disease  is  best  diagnosed  early 
in  the  morning  when  the  dew  is  still  present  on  the 
foliage.  Diseased  parts  have  a  peculiar  violet  tint. 
This  is  due  to  the  downy  cover  of  the  fruit  by  the 
fungus.  Soon  the  affected  leaves  lose  their  green 
color,  becoming  yellow  in  spots,  and  by  the  second 
or  third  day  they  have  all  collapsed,  and  are  entirely 
covered  by  the  downy  fruiting  stalks  of  the  causative 
fungus  (fig.  54  a) .  If  the  weather  is  unfavorable  the 
disease  will  be  seen  to  work  in  restricted  spots  in  the 
field  with  the  tops  of  the  affected  plants  collapsed. 
However,  after  several  days  the  diseased  onions  begin 
to  recover  by  sending  out  new  top  growths.  The 
previously  diseased  leaves  now  dry  and  break  away. 


FIG.  54.     ONION  DISEASES. 

a.   Downy  mildew,  b.  mature  conidiophore  and  conidia  of  Peronospora  schleideni, 

c.  fertilization  of  the  female  oogonium  by  the  male  antheridium,  d.  oospore  (a.  to 

d.  after  Whotzel),  e.  onion  smut,  /.  spore  ball  of  the  smut  fungus,  g.  spore  germina- 
tion, formation  of  sporidia  at  x,  h.  Vermicularia  anthracnose,  *.  section  through 
acervulis  of  Vermicularia  circinans,  j.  setae  and  spore  formation  in  V.  circinans  (e. 
to  g.,  i.  and  j.  after  Thaxter),  k.  pink  root  of  onion,  healthy  and  diseased  bulbs,  I. 
pink  root  of  onion  showing  nipple  formation,  m.  a  formaldehyde  drip  attachment 
to  a  planet  junior  seed  sower,  n.  a  copper  tank  drip  with  flexible  black  tin  tube  and 
valve  (m.  and  n.  after  Stone). 


Family  Liliaceas  287 

The  blight  in  this  case  does  not  entirely  disappear. 
With  the  coming  of  wet  muggy  weather  the  epidemic 
may  begin  a  new  course. 

The  seriousness  of  blight  is  usually  overlooked  by 
growers,  because  it  usually  works  best  when  the 
onions  have  attained  considerable  bottoms.  The 
latter  are  not  disfigured  or  attacked  in  any  way.  But 
there  is  an  indirect  loss  from  the  disease,  because  the 
food  which  is  stored  in  the  leaves  is  eventually  des- 
tined for  the  bulbs.  When  the  foliage  is  destroyed 
there  is  bound  to  be  a  reduction  in  yield  of  market- 
able onions. 

The  Organism.  The  conidiophores  or  fruiting 
stalks  come  out  on  the  surface  through  the  leaf 
stomata  (fig.  54  a).  The  conidia  are  borne  at  the 
tip  end  of  branches  of  the  main  fruiting  stalk.  They 
germinate  by  means  of  a  germ  tube.  The  oospores 
or  sexual  spores  (fig.  54  c,  d)  are  formed  in  the  same 
way  as  in  Pythium.  The  contents  of  the  antheridium 
is  emptied  into  the  oogonium,  and  fertilization  takes 
place.  The  oospore  is  thick  walled,  granular  and  oily 
within.  The  mycelium  of  the  fungus  is  non-septate, 
hyaline,  and  derives  its  food  by  means  of  suckers  or 
haustoria  which  it  sends  to  the  host  cells. 

Control.  Good  results  have  been  obtained  by 
Whetzel1  from  spraying  with  Bordeaux.  The  form- 
ula recommended  is  5-5-50.  The  number  of  appli- 
cations will  vary  with  the  climatic  conditions  and 
with  the  severity  of  the  disease.  It  is  doubtful  if 

1  Whetzel,  H.  H.,  New  York  (Cornell)  Agr.  Expt.  Sta.  Bui.  218  : 
139-161,  1904. 


288  Diseases  of  Truck  Crops 

one  application  will  suffice;  two  to  four  applica- 
tions may  sometimes  be  necessary,  especially  in  low, 
wet,  and  poorly  drained  lands  where  the  disease 
is  severest. 

SMUT 
Caused  by  Urocystis  cepulce  Frost. 

Next  to  blight,  smut  is  the  most  important  disease 
of  the  onion.  The  trouble  is  found  wherever  onions 
are  grown,  and  it  does  not  seem  to  be  limited  by 
climatic  or  soil  conditions. 

Symptoms.  Smut  is  at  first  characterized  by  dark 
spots  on  the  seedling  leaves  (fig.  54  e).  When  held 
up  to  the  light  these  spots  are  opaque.  Later  longi- 
tudinal cracks  appear  on  one  side  of  the  spot,  which 
widen,  exposing  within  a  fibrous  mass  covered  with  a 
black  powder  made  up  of  the  ripe  spores  of  the  fungus. 
Young  infected  seedlings  usually  die  early.  Those 
which  survive  later  show  smut  pustules  on  the  leaves 
and  the  outer  scales  of  the  bulbs.  The  disease  may 
be  carried  from  infected  fields  with  the  seed,  with 
infected  manure,  and  by  man  himself  on  infected  soil 
particles  adhering  to  his  shoes  or  implements. 

The  Organism.  The  spores  of  the  fungus  are  able 
to  retain  their  vitality  for  a  long  time,  possibly 
twelve  years.  The  spore  ball  (fig.  54  f)  is  made  up  of 
sterile  cells  and  spores.  The  latter  (fig.  54  g)  germ- 
inate in  the  same  way  as  spores  of  other  smuts,  see 
corn  smut,  p.  252. 


Family  Liliaceae  289 

Control.  A  very  effective  treatment  is  to  sow  the 
seed  in  a  seed  bed  and  later  transplant  the  sets. 
This  method  not  only  insures  a  crop  free  from  smut, 
but  the  quality  and  the  yield  are  benefited.  An- 
other method  which  generally  gives  good  results  is 
to  apply  to  the  soil  at  sowing  time  from  500  to  700 
gallons  per  acre  of  a  solution  made  up  of  one  pint  of 
formaldehyde  in  thirty  gallons  of  water.  'this  is 
applied  with  a  drip  attachment  of  the  seed  drill. 
For  this  method  to  be  effective  the  soil  must  be  in 
good  condition  of  tilth. 

RUST 
Caused  by  Puccinia  allii  D.  C. 

Rust  is  a  rare  disease  with  onions  in  the  United 
States,  and  very  little  is  known  about  it.  It  is 
doubtful  if  it  will  ever  cause  damage  serious  enough 
to  warrant  treatment. 

ANTHRACNOSE 
Caused  by  Vermicularia  circinans  Berk. 

This  disease  seems  to  be  confined  to  the  bulbs 
only.  It  is  characterized  by  black  spots  (fig.  54  h) 
which  are  made  up  of  various  rings  one  within  the 
other.  Each  ring  consists  of  minute  black  dots, 
which  are  the  acervuli  of  the  fungus  and  which  pos- 
sess numerous  black  hairs  or  bristles  (fig.  54  i,  j). 
19 


290  Diseases  of  Truck  Crops 

It  causes  the  greatest  damage  under  poor  storage 
conditions.     For  methods  of  control,  see  p.  292. 

BOTRYTIS  ROT  (fig.  52  b)  is  a  storage  trouble 
usually  of  little  importance. 

BLACK  MOLD 

Caused  by  Macro sporium   parasiticum   Thuem. ; 
Macrosporium  porri  Ell. 

Black  mold  frequently  follows  injury  from  downy 
mildews  or  any  other  causes  which  weaken  the  plant. 
Spraying  to  control  downy  mildew  will  also  prevent 
this  disease. 

BULB  ROT 
Caused  by  Fusarium  sp. 

This  disease  is  usually  a  storage  trouble;  but  the 
injury  starts  in  the  field  and  is  favored  by  a  wet  sum- 
mer season.  The  rot  is  prevalent  in  Ohio  and  Con- 
necticut and  possibly  also  elsewhere  where  onions  are 
stored  in  bulk.  It  works  inward,  attacking  the  heart 
of  the  bulb  so  that  the  interior  easily  slips  out.  For 
methods  of  control,  see  p.  292. 

SCLEROTIUM   ROT  OR   BLACK  NECK 

Caused  by  Sclerotium  cepivorum  Berk. 

Sclerotium  rot  is  a  serious  storage  trouble  of  white 
onions  in  Ohio.  The  disease  seems  to  be  favored  by 


Family  Liliaceae  291 

improper  storage  conditions,  and  by  early  topping 
in  the  field  where  a  green  neck  offers  a  favorable 
entrance  of  the  rot.  The  latter  is  of  a  dry  nature, 
and  the  affected  bulbs  become  blackened  and 
wrinkled  at  the  neck  (fig.  52  d).  Selby1  recommends 
treating  the  bulbs  with  formaldehyde  gas  as  recom- 
mended for  the  white  potato,  p.  336. 

PINK  ROOT 

Cause  Unknown  fungus.* 

Pink  root  is  a  serious  disease  which  is  threatening 
the  onion  industry  in  the  Laredo  districts  of  Texas, 
The  disease  apparently  is  not  new,  but  it  has  not 
been  investigated  before.  The  work  of  the  writer  is 
as  yet  incomplete,  hence  no  complete  statement  can 
be  made  at  this  time  relative  to  the  disease. 

The  roots  of  affected  sets  first  turn  slightly  yellow- 
ish, when  they  are  known  as  "Yellow  root, "  and  then 
pink.  Affected  roots  dry  up,  and  the  bulbs  con- 
stantly make  an  attempt  to  produce  new  rootlets, 
which  even  under  favorable  conditions  become  pink 
and  die.  At  the  end  of  the  season  and  because  of  the 
attempt  of  the  bulb  to  produce  new  roots,  a  nipple  is 
usually  formed  at  the  bottom  of  the  center  plate  of 
the  bulb  (fig.  54  1  and  k).  The  disease  is  carried  with 
the  young  sets  from  the  seed  beds  to  the  field.  It 

1  Selby,  A.  D.,  Ohio  Agr.  Expt.  Sta.  Bui.  214  :  414,  1910. 
3  Investigations  by  the  author  seem  to  show  that  pink  root  is 
paused  by  a  pathogenic  fungus. 


292  Diseases  of  Truck  Crops 

may  also  be  introduced  with  infected  soils  clinging  to 
the  rootlets  of  the  sets. 

Control.  It  is  severest  in  fields  where  onions  have 
been  grown  too  long  in  the  same  field.  Crop  rotation 
will  not  control  nor  reduce  the  losses  from  pink  root 
in  the  field.  The  use  of  new  land,  especially  for  the 
seed  bed,  is  strongly  urged. 

Pink  root  attacks  the  onion,  chive,  shallot,  garlic, 
and  leek. 

ONION  STORAGE 

Since  the  greatest  profits  are  derived  when  onions 
are  sold  at  a  time  of  greatest  demand,  it  is  necessary 
to  store  the  crop.  In  the  field,  onions  intended  for 
winter  storage  should  be  allowed  to  ripen  well.  The 
degree  of  ripeness  is  indicated  by  a  shriveling  of  the 
tops,  and  when  the  outer  skin  of  the  bulbs  becomes 
dry  before  being  pulled.  The  ripening  process  in  the 
field  may  often  be  hastened  by  rolling  a  light  roller 
on  the  tops  to  break  them.  After  being  pulled,  the 
onions  are  allowed  to  lay  in  the  rows  for  several  days. 
They  are  occasionally  stirred  with  wooden  rakes  to 
encourage  an  even  drying  of  the  bulbs.  After  the 
necks  are  clipped,  the  bulbs  are  put  in  crates  and  are 
either  allowed  to  dry  further  in  the  field  or  they  are 
carried  to  curing  sheds  where  the  crates  remain  for 
about  two  weeks  until  finally  placed  in  storage. 
This  method  is  preferred  by  most  growers,  as  it  is 
not  desirable  to  expose  the  red  and  yellow  varieties 
to  the  full  sunlight  in  the  field,  The  immature, 


Family  Liliaceae  293 

soft,  or  " thick  necks"  should  be  disposed  of  early, 
as  they  keep  very  poorly  in  storage.  Good  storage 
onions  will  rattle  like  wood  blocks  when  poured  out 
from  the  crate. 

After  curing  in  the  sheds,  the  bulbs  are  sorted  over 
on  the  sorting  racks  where  only  the  soundest  are 
stored  away.  »In  some  localities,  onions  are  stored 
in  pits.  This  may  serve  the  purpose  where  only 
small  quantities  are  grown.  On  a  large  scale  storage 
plants  (fig.  52  e— g)  are  in  operation. 

Storage  Conditions.  The  essentials  necessary  in 
storing  onions  are  summarized  by  Beattie1  as  follows: 
"Plenty  of  ventilation,  storing  in  small  quantities, 
a  comparatively  low  temperature,  dryness,  and  safety 
from  actual  freezing. "  The  construction  of  a  storage 
house  is  not  different  from  that  of  a  sweet  potato 
house,  see  p.  182.  The  house  should  be  double 
walled  throughout,  with  plenty  of  felt  or  paper 
lining.  In  this  way  a  dead  air  space  in  all  the 
walls  will  permit  of  more  even  indoor  tempera- 
tures. Top  ventilation  is  provided  by  means  of 
roof  ventilators.  Bottom  ventilation  is  secured 
by  means  of  bottom  windows  or  drain  pipes  built 
into  the  foundation  at  the  surface  of  the  ground. 
A  false  floor  is  also  constructed  inside,  leaving  an 
air  space  of  about  two  to  three  inches  from  the 
main  floor. 

The  temperature  of  the  storage  house  should  be  as 
low  as  possible,  but  kept  above  the  freezing  point, 
i.  e.  above  32  to  36  degrees  F.  During  severe  cold 

1  Beattie,  W.  R.,  U.  S.  Dept.  of  Agr.  Farm.  Bui.  354  :  5-36,  1909, 


294  Diseases  of  Truck  Crops 

weather  all  openings  should  be  closed.  Occasionally 
heat  may  be  necessary  and  this  can  be  applied  by 
stoves.  Onions  are  often  stored  in  bags  or  in  slat 
bins  holding  100  to  300  bushels  each.  However, 
neither  bags  nor  bins  are  satisfactory.  The  best 
method  is  storing  in  crates. 

Of  the  Liliacese  weeds,  the  only  one  of  importance 
is  the  wild  garlic,  Allium  vineale.  It,  however,  is  not 
known  to  harbor  any  of  the  diseases  which  attack 
onions  and  its  other  closely  related  species. 


CHAPTER  XIX 

FAMILY  MALVACE.E 

THIS  important  family  has  but  one  plant  which  is 
of  interest  to  the  trucker,  i.  e.  the  okra.  This  crop 
is  grown  more  in  the  Southern  States.  It  is  to  be 
regretted  that  more  of  the  people  of  the  United  States 
have  not  as  yet  learned  its  great  food  value.  Accord- 
ing to  the  Thirteenth  Census  of  the  United  States  the 
area  devoted  to  okra  in  1909  was  estimated  at  347  acres 
and  the  value  of  the  crops  at  $24,969.  Of  the  few 
States  which  grow  this  crop  may  be  mentioned  Georgia, 
Texas,  Louisiana,  Florida,  and  North  Carolina. 

DISEASES  OF  THE  OKRA  (Hibiscus  esculentus) 

Generally  speaking,  the  okra  may  be  considered  a 
hardy  plant.  But  it  is  subject  to  a  few  diseases  which 
in  severe  cases  may  threaten  the  profitable  raising  of 
the  crop. 

LEAF  SPOT 
Caused  by  Cercospora  hibisci  T.  and  Earle. 

The  disease  seems  to  be  as  yet  restricted  to  Porto 
Rico.  It  is  of  no  economic  importance  in  the  United 

295 


296  Diseases  of  Truck  Crops 

States.  According  to  Stevenson1  the  trouble  ap- 
pears as  indefinite  sooty  patches  (fig.  54  c)  on  the 
lower  surface  of  the  leaves.  This  saps  the  vitality 
of  the  foliage,  causing  it  to  turn  yellow  and  to  drop 
off  prematurely.  Great  care  should  be  exercised  not 
to  allow  the  above  disease  to  gain  a  foothold  in  the 
United  States. 

WILT 

Caused  by  Fusarium  malvacearum  Taub.2 

Wilt  is  perhaps  the  main  drawback  to  okra  culture. 
The  disease  is  found  in  light  sandy  soils,  and  some- 
times seems  to  work  hand  in  hand  with  root  knot. 

Symptoms.  The  disease  does  not  seem  to  attack 
young  seedlings.  It  is  common  on  older  plants,  which 
however  remain  stunted  as  the  disease  works  slowly. 
In  severe  attacks,  however,  the  lower  leaves  wilt, 
droop,  dry,  and  fall  off.  This  is  followed  by  a  droop- 
ing, wilting,  and  falling  off  of  the  upper  foliage,  leav- 
ing thus  a  bare  stalk,  which  eventually  dries  up.  On 
pulling  up  a  diseased  plant,  we  find  that  the  root 
system  is  apparently  sound.  But  on  splitting  a 
diseased  root  and  stem  lengthwise  the  interior  fibro- 
vascular  bundles  are  found  to  be  brown,  indicating 
that  the  seat  of  the  trouble  is  there  localized. 

The  Organism.  Unpublished  work  by  the  author 
has  definitely  established  that  okra  wilt  is  caused  by 

1  Stevenson,  J.  A.,  Jour.  Dept.  Agr.  of  Porto  Rico,  1 :  93-117, 1917. 

2  From  unpublished  work  by  the  writer. 


FIG.  55.     DISEASES  OF  THE  OKRA. 

a.  Okra  field  badly  affected  with  the  Texas  Root 
rot,  to  the  front  two  resistant  hills,  b.  root  knot, 
c.  Cercospora  leaf  spot. 


Family  Malvaceae  297 

a  new  species  of  Fusarium,  technically  named  F. 
malvacearum.  The  okra  wilt  is  distinct  and  different 
from  the  wilt  of  cowpea,  cotton,  or  watermelon,  all 
of  which  are  caused  by  distinct  species  of  Fusaria. 
A  full  description  of  the  organism  will  soon  appear 
elsewhere. 

Control.  The  only  remedy  known  for  this  disease 
is  crop  rotation.  Since  okra  wilt  attacks  only  the 
okra<  any  other  truck  crop  may  be  used  in  the  rota- 
tion system.  It  is  also  probable  that  wilt  may  be 
controlled  by  the  development  of  resistant  varieties. 

ROOT  ROT,  see  RHIZOCTONIA,  p.  45. 

TEXAS  ROOT  ROT 
Caused  by  Ozonium  omnivorum  Shear. 

Texas  root  rot  is  a  disease  which  is  perhaps  of 
equal  importance  with  wilt.  The  disease  is  not  found 
on  sandy  soils,  but  on  okra  grown  on  the  typical 
waxy  heavy  lands  such  as  are  found  in  Texas.  It 
appears  after  a  rain  or  after  irrigation. 

Symptoms.  The  trouble  does  not  appear  until  the 
plants  have  begun  to  bloom.  At  this  stage  infected 
plants  suddenly  wilt  and  the  foliage  drops  off  (fig. 
54  a).  On  pulling  out  a  diseased  plant,  we  find  that 
the  trouble  is  localized  at  the  crown  and  root  of  the 
plant.  The  infected  surface  is  darkened,  shrunken, 
but  softened,  so  that  the  epidermis  may  be  easily 
peeled  off  from  the  roots  and  crown  of  the  plant. 
Occasionally,  the  diseased  parts  are  covered  with 


298  Diseases  of  Truck  Crops 

minute  warts  consisting  of  whitish  to  yellowish  fun- 
gus threads.  Very  often  in  pulling  out  a  plant 
which  is  partly  infected,  the  young  healthy  rootlets 
or  even  those  which  are  partly  destroyed  are  found 
to  be  colored  pinkish  buff. 

The  Organism.  The  organism  which  causes  Texas 
root  rot  is,  as  far  as  we  know,  sterile.  By  this  is 
meant  that  the  fungus  reproduces  by  division 
and  further  growth  of  its  mycelium,  but  produces 
no  fruit  (fig.  28  q  and  r).  Duggar1  claims  that  the 
pink  buff  color  mentioned  above  represents  the 
colored  spore  masses  of  the  fungus  which  he  named 
Phymatotrichum  omnivorum  (Shear)  Dug.  However 
no  inoculation  experiments  have  been  carried  out  to 
prove  that  this  fruiting  stage  is  in  any  way  connected 
with  Ozonium.  In  establishing  the  relationship  of 
various  stages  of  apparently  the  same  parasitic  fun- 
gus, inoculation  experiments  alone  should  be  the 
crucial  test. 

Control.  No  definite  methods  of  control  are  as 
yet  known.  Deep  plowing  undoubtedly  retards  the 
work  of  the  disease,  but  it  does  not  prevent  it  by  any 
means.  Crop  rotation  should  be  resorted  to.  In  the 
system  of  rotation  may  be  included  sweet  corn,  cab- 
bage, radish,  spinach,  kale,  mustard,  lettuce,  and 
cauliflower.  Crops  to  be  omitted  from  the  rotation 
are  beans,  beets,  cowpeas,  sweet  potatoes,  eggplants, 
tomatoes,  and  peppers.  The  latter  two  are  only 
partly  susceptible  to  Texas  root  rot. 

ROOT  KNOT  (fig.  54  b),  see  NEMATODE,  p.  49. 

1  Duggar,  B.  M.,  Ann.  Missouri  Bot.  Gard.,  3:  11-23,  1916. 


CHAPTER  XX 

FAMILY    PORTULACACE^: 

IN  this  family  the  only  plant  which  may  interest 
the  trucker  is  the  purslane.  The  latter  is  grown  as  a 
pot  herb;  but  it  is  little  known  in  the  United  States. 
It  is  comparatively  free  from  diseases,  only  two  of 
which  need  be  mentioned. 

WHITE  RUST 
Caused  by  Cystopus  portulacece  (D.  C.)  Kze. 

In  appearance,  this  rust  is  not  different  from  the 
white  rust  of  the  radish.  However  the  causative 
fungus  is  not  the  same.  White  rust  is  not  prevalent 
in  the  United  States  and  is  of  no  economic  importance. 

ROOT  ROT,  see  RHIZOCTONIA,  p.  45. 

Weeds.  There  are  no  weeds  of  importance  in  the 
Portulacaceae  family  which  carry  diseases  detrimental 
to  truck  crops. 


299 


CHAPTER  XXI 

FAMILY  SOLANACE^E 

IN  this  great  family  the  trucker  possesses  crops 
which  are  of  great  economic  importance.  Some  of 
them  are  the  eggplant,  pepper,  potato,  and  tomato. 
According  to  the  Thirteenth  Census  of  the  United 
States,  the  total  area  devoted  to  eggplants  in  1909 
was  895  acres,  and  the  crop  value  was  estimated  at 
$154,643.  The  two  States  which  supply  nearly  all 
the  markets  with  eggplant  are  Florida  and  New 
Jersey.  The  total  area  in  1909  devoted  to  peppers 
was  estimated  at  3,483  acres  and  the  crop  valued 
at  $408,741.  Of  the  leading  States  producing  this 
crop  are  New  Jersey,  California,  Florida,  New 
Mexico,  Illinois,  Texas,  and  Louisiana.  The  area  in 
white  potatoes  in  1909  was  estimated  at  3,668,855 
acres,  and  the  crop  valued  at  $166,423,910.  The 
leading  potato  States  are  New  York  and  Michigan; 
the  others  following  in  their  order  are:  Wisconsin, 
Pennsylvania,  Minnesota,  Ohio,  Iowa,  Illinois,  Maine, 
Nebraska,  Colorado,  Indiana,  Missouri,  Virginia, 
New  Jersey,  Kansas,  California,  Washington,  Ken- 
tucky, North  Dakota,  South  Dakota,  Oregon,  West 
Virginia,  Tennessee,  Maryland,  Texas,  Oklahoma, 

300 


Family  Solanaceae  301 

Arkansas,  Idaho,  Vermont,  Massachusetts,  Connec- 
ticut, Montana,  Louisiana,  New  Hampshire,  Ala- 
bama, Utah,  Georgia,  Delaware,  South  Carolina, 
Florida,  Mississippi,  Wyoming,  New  Mexico,  Nevada, 
Rhode  Island,  and  Arizona.  The  area  in  1909  de- 
voted to  tomatoes  was  estimated  at  207,379  acres, 
and  the  crop  valued  at  $13,707,929.  The  leading 
producing  States  are  as  follows:  Maryland,  New 
Jersey,  Indiana,  Delaware,  Florida,  Virginia,  Mis- 
souri, New  York,  Ohio,  Texas,  California,  Tennessee, 
Pennsylvania,  Illinois,  Mississippi,  Kentucky,  Michi- 
gan, Iowa,  West  Virginia,  Arkansas,  Colorado,  Utah, 
Kansas,  and  Massachusetts.  States  with  less  than 
one  thousand  acres  are  omitted. 

DISEASES  OF  THE  ^EGGPLANT  (Solanum 
melongena) 

SOUTHERN  WILT,  see  TOMATO,  p.  342. 
DAMPING  OFF,  see  PYTHIUM,  p.  43. 

FRUIT  ROT 
Caused  by  Phomosis  vexans  (Sacc.  and  Syd.)  Hart. 

The  disease  is  quite  common  in  New  Jersey,  and  it 
undoubtedly  occurs  in  the  more  southern  States. 
The  trouble  has  been  recognized  as  serious,  but  the 
cause  has  been  only  recently  worked  out  by  Harter.  * 

Symptoms.    Fruit  rot  attacks  all  parts  of  the  plant 

1  Harter,  L.  L.,  U.  S.  Dept.  of  Agr.  Jour.  Agr.  Research,  2  : 331- 
338. 


302  Diseases  of  Truck  Crops 

except  the  roots.  On  the  seedlings  it  causes  a  damp- 
ing off.  Young  plants  are  attacked  at  the  stem  end 
or  an  inch  or  two  above  the  ground  line  as  indicated 
by  a  constricted  area  at  that  place.  On  the  leaves  the 
trouble  is  manifested  as  large  brown  round  spots 
which  later  become  irregular  and  jagged  (fig.  56  a). 
The  older  spots  are  light  purple  in  the  center  and 
surrounded  by  a  black  margin.  As  they  enlarge  the 
spots  also  invade  the  veins,  midribs,  and  petioles, 
forming  depressions.  Diseased  fruits  are  at  first 
soft  and  mushy,  but  later  they  become  dry,  shriveled, 
and  mummified  (fig.  56  b). 

The  Organism.  Pycnidia  (fig.  56  f)  are  usually 
found  on  all  parts  of  the  plant  attacked.  Within 
the  body  of  the  pycnidia^and  intermixed  with  the 
conidiophores  (fig.  56  c)  and  pycnospores  (fig.  56  e), 
are  found  filiform  hooked-shaped  bodies  termed  stylo- 
spores  (fig.  56  d).  Phomosis  vexans  has  been  erroni- 
ously  referred  to  as  Phoma  solani  Hals;  Phoma  vexans 
Sacc.  and  Syd.,  and  Aschochyta  hortorum  Speg. 

Control.  The  seedlings  in  the  seed  bed  should  be 
sprayed  with  Bordeaux  at  least  once  before  trans- 
planting. The  plant  in  the  field  should  be  sprayed 
from  four  to  eight  times  with  either  Bordeaux  mixture 
or  ammoniacal  copper  carbonate. 

ANTHRACNOSE 
Caused  by  Gleosporium  melongence  E.  and  H. 

Anthracnose  on  the  eggplant  attacks  only  the 
fruit.  The  trouble  is  characterized  by  numerous 


FIG.  56.    EGG-PLANT  DISEASES. 

a.  Phomopsis  of  leaf,  b.  Phomopsis  on  fruit,  c.  conidiophores,  d.  stylospores,  e. 
pycnospores  of  Phomopsis  vexans,  f.  photomicrograph  of  a  cross  section  through  an 
infected  calyx  of  an  egg  plant  showing  pycnidia  of  P.  vexans  (c.  to/,  after  Harter), 
t>.  anthracnose  on  egg-plant  fruit. 


Family  Solanaceae  303 

deep  pits  which  later  become  covered  with  salmon 
colored  acervuli  (fig.  56  g) .  The  latter  are  made  up 
of  myriads  of  spores  of  the  fungus.  Spraying  for 
fruit  rot  will  also  help  to  control  anthracnose. 

STEM  ANTHRACNOSE,  see  POTATO,  p.  324. 

SOUTHERN  BLIGHT,  see  PEPPER,  p.  305. 

ROOT  KNOT,  see  NEMATODE,  p.  49. 

DISEASES  OF  THE  PEPPER  (Capsicum  annum) 

The  pepper  plant  is  considered  comparatively 
hardy,  and  its  few  diseases  usually  become  trouble- 
some only  when  the  crop  is  grown  too  long  on  the 
same  land. 

ANTHRACNOSE 
Caused  by  Glomerella  piper ata  (  E.  and  E.)  S. 

Anthracnose  is  a  serious  disease  which  is  usually 
confined  to  the  fruit  only.  Its  symptoms  are  char- 
acterized by  round,  soft,  sunken,  pale  spots  (fig.  57  a). 
The  summer  or  conidial  stage  is  known  as  Gleospo- 
rium  piper  alum  E.  and  E.  and  is  found  as  salmon 
colored  pustules  abundantly  scattered  over  the  spots 
(fig.  57  b-f).  The  ascospore  stage  may  develop  in 
pure  cultures  of  the  fungus. 

BLACK  ANTHRACNOSE 
Caused  by  Colletotrichum  nigrum  E.  and  H. 

This  form  of  anthracnose  differs  from  the  disease 
described  above  only  in  that  the  spots  turn  jet  black. 


304  Diseases  of  Truck  Crops 

The  trouble  attacks  the  young  as  well  as  the  mature 
fruit.  The  winter  or  ascospore  stage  of  the  causative 
fungus  has  not  as  yet  been  found.  It  is  very  prob- 
able that  the  fungus  is  carried  over  as  viable  myce- 
lium on  the  infected  fruit  left  over  in  the  field.  Both 
forms  of  anthracnose  may  be  controlled  by  spraying 
with  Bordeaux  mixture. 

FRUIT  SPOT 
Caused  by  Macrosporium  sp. 

This  disease,  which  is  as  important  as  anthracnose, 
attacks  the  fruit  at  the  blossom  end.  Attacked 
peppers  are  half  rotted,  black,  and  moldy.  Little 
is  known  about  the  causative  fungus.  It  is  probable 
that  the  disease  has  the  same  origin  as  the  blossom 
end  rot  of  tomatoes,  and  that  the  Macrosporium 
fungus  is  only  secondary.  Spraying  with  Bordeaux 
is  recommended. 

LEAF  SPOT 
Caused  by  Cercospora  capsisi  H.  and  W. 

This  disease  is  prevalent  on  peppers  in  Texas.  The 
same  trouble  may  be  found  also  in  the  more  southern 
States.  It  is  characterized  by  roundish  raised  spots 
on  the  upper  surface,  at  first  brown,  later  becoming 
gray  brown.  They  are  limited  by  a  dark  zone,  be- 
yond which  the  leaf  tissue  is  pale  and  chlorotic. 
Where  the  spots  are  abundant  the  leaves  turn  yellow, 
wilt,  and  fall  off  prematurely. 


FIG.  57.     DISEASES  OF  THE  PEPPER. 

a.  Anthracnose  on  fruit,  b.  anthracnose  spot  showing  acervuli,  c.  acervulus 
greatly  magnified,  d.  section  through  acervulus  of  Glomerella  piperata,  showing  setae, 
conidiophores,  and  conidia,  e.  conidia,  /.  germinating  conidium,  g.  Southern  blight. 


Family  Solanaceae  305 

The  conidiophores  of  the  fungus  are  formed  in 
clusters  on  both  surfaces  of  the  spots.  The  conidia 
are  dilutely  brown,  clavate,  and  several  septate. 

SOUTHERN  BLIGHT 
Caused  by  Sclerotium  Rolsfsu  Sacc. 

Blight  is  a  disease  which  is  commonly  met  with  in 
the  Southern  States.  It  often  causes  considerable 
losses,  owing  to  the  fact  that  a  great  percentage  of  the 
plants  is  killed  at  the  bearing  age. 

Symptoms.  Affected  plants  become  apparent  by 
the  drooping  of  the  young  leaves  at  the  tips  of  the 
branches.  At  night  the  plant  recovers  and  it  appears 
normal  the  next  morning.  This,  however,  is  a  tem- 
porary condition.  Wilting  generally  progresses,  and 
after  three  to  four  days  the  leaves  yellow  completely, 
wilt,  droop,  and  die.  In  another  day  the  stem  of  the 
plant  loses  its  green  color,  dries,  and  dies.  On  pull- 
ing out  a  plant  freshly  wilted,  we  find  a  shrunken 
discolored  area  at  the  foot  of  the  stem,  slightly  be- 
low ground  level.  In  more  advanced  stages,  the 
shrunken  area  is  covered  by  a  delicate  web  of  white 
mycelial  threads  (fig.  57  g),  and  after  the  death  of 
the  plant  numerous  brown  mustardlike  sclerotia  are 
found  on  the  surface  of  the  affected  tissue. 

The  seriousness  of  blight  is  that  it  attacks  not  only 
the  pepper  but  also  the  tomato,  eggplant,  Irish  po- 
tato, sweet  potato,  beets,  beans,  cowpeas,  cabbage, 
squash,  watermelon,  rhubarb,  and  numerous  other 
plants. 


306  Diseases  of  Truck  Crops 

Control.  It  may  be  controlled  in  a  way  similar  to 
that  recommended  for  lettuce  drop,  see  p.  143. 

DISEASES  OF  THE  POTATO  (Solanum 
tuberosum) 

General  Consideration.  Potato  diseases  are  caused 
for  the  most  part  by  definite  parasitic  organisms. 
However,  there  are  many  indirect  causes  which  may 
predispose  the  plant  to  various  diseases. 

Color.  The  shade  of  red  or  pink  in  the  tuber  is 
usually  affected  by  the  health  of  the  plant  and  by  its 
nutrition.  Color  is  usually  intensified  in  run  out 
stock.  The  White  Ohios,  for  instance,  may  show 
much  red  at  the  eyes  and  at  the  eye  end  under  poor 
conditions,  but  are  white  under  proper  culture  and 
climate.  Deep  eyed  and  poor  shaped  tubers  are 
likely  to  be  densely  colored.  The  flesh  of  the  Early 
Rose  variety  may  become  red  under  unfavorable 
conditions.  Whiteness  of  flesh  is  also  influenced  by 
the  degree  of  ripeness.  The  color  therefore  may 
often  serve  as  a  general  indicator  of  the  health  of  the 
tuber.  Sharp  and  long  eyed  ends  with  numerous 
eyes  usually  indicate  a  weak  and  run  out  strain. 

Position  of  the  Eyes.  On  examining  a  tuber,  we 
find  a  cluster  of  well  developed  eyes  at  the  blossom 
end,  generally  termed  the  "seed  end. "  The  other  is 
generally  known  as  the  "stem  end"  of  the  tuber  and 
it  contains  but  few  if  any  of  the  eyes.  Careful 
growers  are  in  the  habit  of  discarding  the  "stem 
ends. "  Plants  resulting  from  the  stem  ends  develop 


Family  Solanacese  307 

late  and  are  poor  yielders.  On  the  other  hand,  plants 
resulting  from  the  "seed  ends"  develop  early,  are 
much  more  prolific  and  vigorous,  apparently  more 
resistant  to  disease  and  less  subject  to  running  out. 
Market  gardeners  who  aim  at  producing  an  early 
crop  should  depend  on  the  "seed  ends"  for  plant- 
ing, and  should  discard  the  "stem  ends,"  and  even 
those  pieces  which  come  from  the  middle  of  the  seed 
tuber. 

It  is  common  knowledge  that  potatoes  soon  run 
out  when  grown  too  long  under  Southern  conditions. 
In  the  South,  Northern  grown  seed  must  be  de- 
pended upon,  such  seed  being  far  superior  to  that 
grown  in  the  South.  The  effect  of  one  year's  removal 
of  the  Northern  seed  to  Southern  conditions  is  notice- 
able in  a  decline  in  yield  and  vigor  of  the  crop. 
Therefore  except  under  favorable  Northern  latitudes, 
frequent  changes  of  seed  are  necessary. 

Germination  Troubles.  Conditions  of  poor  germi- 
nation are  often  met  with.  There  may  be  several 
factors  to  account  for  this.  When  planting  seed 
which  is  heavily  infected  with  blackleg,  wilt,  or 
Rhizoctonia  rot,  a  poor  germination  and  stand  should 
be  expected.  This  is  especially  true  in  cool,  damp 
springs. 

Cutting  the  seed  ten  or  fifteen  days  before  plant- 
ing, as  is  the  custom  with  some  growers,  is  a  practice 
which  may  lead  to  much  germination  trouble.  When 
this  is  done,  the  seed  is  held  too  long  and  is  apt 
to  undergo  a  heat.  Frequently  seed  is  cut  too 
small  and  there  are  few  or  no  eyes  left  to  permit 


308  Diseases  of  Truck  Crops 

germination.  Poor  sprouting  may  sometimes  be 
attributed  to  shipping  of  seed  in  overheated  cars. 
In  this  ease  the  seed  when  cut  open  will  be  seen  to  be 
blackened  at  the  heart,  a  trouble  soon  to  be  con- 
sidered. 

LEAF  ROLL 
Cause  Unknown. 

Leaf  roll  is  but  an  old  disease  with  a  new  name. 
The  trouble  has  been  carefully  studied  by  Orton. x 

Symptoms.  As  the  name  indicates,  the  charac- 
teristic symptom  is  a  rolling  of  the  leaves  (fig.  58  a). 
The  leaflets  roll  and  curl  upward  on  their  midrib, 
often  assuming  a  tube  shape.  This  condition  may 
involve  the  upper  leaves  of  a  plant  or  in  serious  cases 
the  entire  foliage.  Rolled  leaflets  assume  a  sickly 
yellow  reddish  to  purplish  color.  This  is  especially 
apparent  on  affected  plants  grown  from  tubers  of  a 
previously  infected  crop. 

The  effect  of  leaf  roll  is  to  interfere  with  proper 
growth.  This  generally  results  in  a  premature  dying 
of  the  leaves.  The  effect  of  the  disease  on  the  tubers 
seems  to  be  strongly  marked.  The  tubers  in  the  hill 
are  small,  unfit  for  market  and  the  yield  is  often  re- 
duced by  about  one  half.  The  disease  is  not  con- 
tagious in  the  sense  that  it  can  spread  from  plant  to 
plant;  but  the  inherent  weakness  is  transmitted  to 
the  seed.  This  when  sown  again  will  show  new  out- 
breaks of  leaf  roll  the  following  year.  True  leaf  roll 

«  Orton,  W.  A.,  U.  S.  Dept.  of  Agr.  Bui.  64  :  1-48, 1914. 


FIG.  58.    POTATO  DISEASES. 

a.  Leaf  roll,  b.  curly  dwarf  (a.  and  6.  after  Appel),  c.  net  necrosis,  d.  spindly  sprout, 
e.  black  heart,  /.  hollow  heart  (d.  to  /.  after  Stakman  and  Tolaas),  g.  mosaic,  h.  tip 
burn  (c.  g.  and  h.  after  W.  A.  Orton). 


Family  Solanacese  309 

should  not  be  mistaken  for  a  temporary  rolling  of  the 
leaves  that  may  be  brought  about  by  excessive 
humidity  in  poorly  drained  lands.  Heat,  drought, 
and  excessive  use  of  fertilizers,  especially  potash,  may 
bring  about  a  temporary  leaf  rolling.  Leaf  roll  is 
prevalent  in  Germany,  Austria-Hungary,  Switzer- 
land, the  Netherlands,  Denmark,  and  Sweden.  In 
the  United  States  it  is  found  in  Eastern  Colorado, 
Western  Nebraska,  Virginia,  and  Maine.  Since  the 
trouble  is  carried  with  the  seed,  this  should  be 
secured  from  localities  known  to  be  free  from  the 
disease. 

CURLY-DWARF 

Cause  Unknown. 

This  disease  differs  from  leaf  roll  by  a  dwarfed 
development  of  the  plant,  and  a  wrinkled  and  down- 
ward curling  of  the  leaves  (fig.  58  b),  resembling  the 
natural  curling  of  the  foliage  of  kale  or  Savoy  cab- 
bage. A  peculiarity  of  this  disease  is  that  the  mid- 
ribs, veins,  and  leaf  petioles  together  with  stems  and 
branches  are  all  dwarfed,  giving  the  foliage  a  thickly 
clustered  appearance.  The  foliage  keeps  its  normal 
color  and  turgidity.  There  is  also  a  tendency  for  the 
plant  to  send  out  numerous  branches  with  brittle 
stems.  The  effect  of  the  disease  is  to  reduce  the 
yield,  and  in  severe  cases  there  is  an  absence  of  tuber 
production  altogether.  Like  leaf  roll  the  disease 
is  transmitted  with  the  seed  tubers,  but  it  does  not 
spread  from  plant  to  plant.  The  trouble  is  prevalent 


3io  Diseases  of  Truck  Crops 

in  potato  fields,  but  not  to  such  an  extent  as  to  be 
noticed.  It  is  always  found  scattered  in  individ- 
ual plants,  indicating  deterioration.  Prevention  of 
this  trouble  consists  in  careful  selection  of  seed  from 
unaffected  hills. 

SPINDLING  SPROUT 
Cause  Unknown. 

Spindling  sprout  is  an  abnormality  common  to 
Southern  grown  seed,  which  reduces  the  yield  con- 
siderably. Instead  of  healthy  sprouts,  long,  thin 
slender  ones  germinate  (fig.  58  d) .  No  lesions  of  any 
kind  are  found  on  the  sprouts  or  on  the  seed  pieces. 
A  weak  tuber  will  produce  only  spindly  sprouts.  Both 
strong  and  spindly  sprouts  are  never  found  on  the 
same  seed  tuber.  The  character  and  the  fertility  of 
the  soil  seem  to  have  no  influence  whatsoever  on  this 
trouble.  The  only  remedy  known  is  the  use  of 
Northern  grown  seed. 

INTERNAL  BROWN  SPOTTING 
Cause  Unknown. 

This  disease  is  peculiar  to  the  Early  Maine  and  is 
found  in  New  York,  Maine,  Connecticut,  and  Minne- 
sota. 

Symptoms.  Usually  the  trouble  is  internal  with- 
out any  symptoms  apparent  on  the  outside  of  the 
tuber.  But  occasionally  its  presence  is  indicated  by 


Family  Solanaceae  311 

reddish  discoloration  on  the  skin.  In  cutting  across 
an  affected  tuber,  the  flesh  is  found  to  be  spotted 
reddish  in  isolated  and  scattered  places.  The 
trouble  usually  starts  at  the  stem  end  and  works 
toward  the  bud  end  and  inwards.  In  severe  cases, 
the  trouble  is  indicated  by  a  discolored  band,  the 
outside  of  which  may  easily  be  mistaken  for  late 
blight  injuries,  Phytophora  infestans. 

NET  NECROSIS 
Cause  Unknown. 

Tubers  often  show  minute  black  areas  (fig.  58  c) 
beginning  near  the  stem  end  and  extending  about  an 
inch  inwards.  It  is  not  known  whether  the  trouble, 
if  such  it  may  be  called,  has  any  influence  in  reducing 
the  yield.  However,  it  is  safer  not  to  use  tuber 
seed  which  shows  these  minute  internal  browned 
specks. 

BLACK  HEART 
Caused  by  Overheating. 

This  trouble  is  often  met  on  tubers  kept  in  storage 
pits  which  are  poorly  ventilated.  In  this  case  the 
sweating  and  overheating  will  cause  the  tubers  to 
turn  black  at  the  heart  (fig.  58  e) .  The  same  occurs 
when  potatoes  are  shipped  in  overheated  cars.  The 
remedy  is  to  keep  the  potatoes  as  cool  as  possible, 
and  slightly  above  the  freezing  point. 


312  Diseases  of  Truck  Crops 

HOLLOW  HEART 
Cause  Uneven  Growth. 

When  potatoes  are  overgrown  or  when  quick  growth 
results  from  dry  spells  followed  by  moist  weather, 
the  heart  of  the  tuber  tears  and  a  hollow  center  is 
formed  (fig.  58  f).  The  trouble  does  not  injure  the 
edible  quality  of  the  tuber.  Varieties  such  as  Rural 
New  Yorker  and  King  are  especially  susceptible  to 
hollow  heart.  So  far  as  possible  these  should  be 
avoided  on  heavy  soils. 

TIP  BURN 

Caused  by  Unfavorable  Soil  and  Weather. 

This  trouble  is  prevalent  in  dry  weather  in  mid- 
summer, when  the  leaves  transpire  water  more 
rapidly  than  the  roots  can  take  it  in  from  the  soil. 
As  a  result  the  tips  and  margins  of  the  leaves  dry 
up  and  die  (fig.  58  h) .  The  uprolling  of  the  margins 
of  the  leaflets  is  a  characteristic  of  tip  burn,  also 
distinguishing  it  from  late  blight.  The  trouble  may 
be  considerably  reduced  by  frequent  shallow  culti- 
vation, making  a  shallow  surface  mulch  which  will 
prevent  excessive  evaporation.  Spraying  will  also 
protect  the  foliage  from  tip  burn. 

MOSAIC 

Cause  Unknown. 

Mosaic  is  a  disease  which  is  not  confined  to  the 
tubers,  but  which  also  affects  the  parts  of  the  plant 


Family  Solanaceac  313 

above  ground.  It  is  characterized  by  a  mottled  ap- 
pearance of  the  leaves  (fig.  58  g).  The  portions 
which  are  lighter  in  color  seem  to  be  thinner  than 
those  which  are  of  a  normal  green.  In  advanced 
stages,  brown  spots  of  dead  tissue  may  take  the  place 
of  the  light  colored  mottled  leaf  areas. 

Mosaic  undoubtedly  reduces  the  yield,  the  losses 
often  amounting  to  twenty  per  cent.  The  Green 
Mountain  seems  to  be  very  susceptible  to  mosaic, 
while  the  Irish  Cobler  seems  to  be  especially  resistant. 
It  has  been  proven  by  Worthley1  that  the  disease  is 
carried  with  the  tubers  from  diseased  vines.  As  a 
matter  of  precaution  these  tubers  should  not  be  used 
for  seed.  Long  before  digging,  the  field  should  be 
carefully  inspected,  and  hills  which  show  mosaic 
infection  should  be  pulled  out  and  removed.  This 
will  prevent  tubers  from  diseased  plants  from  being 
mixed  with  healthy  ones. 

ARSENICAL  INJURY 

Potato  foliage  is  often  injured  when  the  plants  are 
sprayed  with  Paris  green.  Within  a  few  days  dead 
spots  similar  to  those  occurring  in  early  blight  ap- 
pear on  the  surface  of  the  leaves.  To  obviate  this, 
lime  should  be  added  to  the  Paris  green.  If  the 
Paris  green  is  used  dry,  one  pound  of  powdered  lime 
should  be  mixed  with  each  half  pound  of  Paris  green. 
The  same  proportions  are  used  when  Paris  green 
is  applied  as  a  spray. 

Pox  or  PIT  (fig.  60)  see  SWEET  POTATO,  p.  152. 

1  Worthley,  E.  I.,  Science,  N.  S.,  42  :  460-461, 1915. 


314  Diseases  of  Truck  Crops 

POWDERY  SCAB 
Caused  by  Spongospora  subterranea  (Woll.)  Johns. 

Powdery  scab  may  justly  be  considered  a  danger- 
ous disease.  The  trouble  has  undoubtedly  been  of 
European  origin.  In  the  United  States  the  disease 
is  now  found  in  Presque  Isle,  Me.,  Chateaugay,  N.  Y., 
Nehalem,  Ore.,  Hastings,  Fla.,  Inohomish,  Wash., 
and  Virginia,  Minn.  The  trouble  has  been  carefully 
investigated  by  Melhus  and  Rosenbaum.1 

Symptoms.  Powdery  scab  attacks  the  young  root- 
lets, forming  galls  resembling  in  size  those  of  legume 
nodules  (fig.  59  c,  d).  At  this  stage  infection  does  not 
take  place  on  the  tubers.  In  fact  it  is  not  unusual 
to  find  the  total  root  system  affected  with  galls,  while 
the  tubers  remain  free.  Thus  if  we  look  for  the  dis- 
ease in  the  field  a  search  should  be  made  for  infection 
on  the  roots  and  rootlets. 

Infection  on  the  tubers  is  evidenced  at  first  by 
minute  discolored  areas  on  the  epidermis.  Six  to 
eight  days  later,  the  spots  increase  in  size,  become 
raised  and  somewhat  jelly  like.  Powdery  scab  on  the 
tubers  cannot  easily  be  mistaken  for  common  scab, 
Actinomyces  chromo genus.  In  powdery  scab  the 
sori  are  more  often  circular  and  not  as  extended  as  in 
common  scab.  In  powdery  scab,  the  border  of  the 
pustules  is  virtually  raised,  forming  a  cuplike  sorus 
or  pit  (fig.  59  a),  and  the  pits  are  deeper  and  at  matu- 

1  Melhus,  I.  E.,  and  Rosenbaum,  J.,  U.  S.  Dept.  of  Agr.  Jour.  Agr. 
Research,  7  :  213-254,  1911. 


a 


g 


FIG.  59.     DISEASES  OF  THE  POTATO. 


a.  Powdery  scab,  early  stage,  b.  powdery  scab,  advanced  stage  of  rotting,  c.  and  d. 
powdery  scab,  gall-forming  stage  on  potato  roots  (c.  and  d.  after  Melhus  and  Rosen- 
baum),  e.  single  potato  cell  showing  spore  balls  of  the  powdery  scab  fungus  (after 
Melhus),  /._  black  leg,  _g.  common  scab,  h.  to  i.  drawings  of  the  organism  of  common 
scab,  showing  branching  of  threads  and  groups  of  spores  or  conidia  (after  Lutman 
and  Cunningham). 


*        ** 

* 


-,'**    *i  «**  %•    - 

* 


FIG.  60.     Pox  OR  PIT  OF  THE  WHITE  POTATO,  SHOWING   DIFFERENT 
STAGES  OF  INFECTION. 


Family  Solanaceae  315 

rity  always  filled  with  black  spore  balls.  The  sori 
of  common  scab  are  shallow  and  made  up  of  corky 
compact  tissue.  After  being  handled  or  shipped  long 
distances,  potatoes  infected  with  powdery  scab  can- 
not be  distinguished  from  those  suffering  from  com- 
mon scab.  However,  a  microscopical  examination 
of  the  sori  will  soon  reveal  the  difference. 

In  storage,  potatoes  infected  with  powdery  scab 
will  dry  rot.  This  is  but  the  final  stage  of  the  disease 
(fig.  59  b) .  While  it  is  not  uncommon  for  the  dry  rot 
to  invade  the  whole  tuber,  it  generally  extends  only  in 
spots.  The  effect  of  powdery  scab  on  stored  potatoes 
is  a  more  rapid  drying  of  the  tubers  and  the  opening 
of  a  way  for  the  invasion  of  secondary  infection. 

In  the  field,  the  disease  is  favored  only  by  cool, 
damp,  and  rainy  weather.  Besides  the  potato,  the 
tomato  too  is  attacked  by  powdery  scab.  In  this 
case,  infection  is  confined  to  the  root  system,  which 
is  much  more  distorted  than  is  the  case  with  the  po- 
tato. Of  the  other  hosts  affected  may  be  mentioned 
Solanum  warscewicii,  S.  hematoclodum,  S.  mammosum, 
S.  marginatum,  S.  ciliatum,  and  S.  commersoni. 

The  Organism.  The  plasmodium  within  the  host 
cells  is  irregular  in  shape.  It  is  composed  of  proto- 
plasm within  which  are  evenly  distributed  nuclei. 
Within  the  host  cell  the  protoplasm  of  the  plasmodium 
is  closely  applied  to  the  host  nucleus.  Infection 
seems  to  take  place  by  means  of  a  plasmodium  rather 
than  by  single  amoebae.  The  parasite  is  confined  to 
the  phloem  of  the  host.  The  invaded  cells  are  not 
killed,  but  are  stimulated  to  an  abnormal  cell  division. 


316  Diseases  of  Truck  Crops 

Germination  of  the  spore  balls  may  be  effected  in 
two  ways:  (i)  the  spore  walls  of  the  entire  spore  balls 
break  down,  liberating  as  many  amoebae  as  there  were 
cells  within;  (2)  the  amoebae  may  escape  through 
openings  in  the  wall  of  the  spore  ball  and  move  about 
by  means  of  pseudopodia. 

Control.  Infected  soils  should  never  be  limed, 
since  the  application  of  lime  favors  the  disease. 
Rotation  of  crops  is  suggested.  The  land  should  be 
given  a  rest  from  potatoes,  or  tomatoes,  for  at  least 
five  years.  Since  infection  of  the  tubers  takes  place 
late,  early  harvesting  and  the  growing  of  early 
maturing  varieties  is  advisable.  Since  the  disease 
is  carried  with  infected  seed  tubers,  the  latter  should 
be  disinfected.  The  use  of  mercuric  chloride  or 
formaldehyde,  or  both,  is  recommended.  (See  also 
P-  336.)  No  soil  treatment  will  cure  the  trouble,  but 
sulphur  applied  at  the  rate  of  nine  hundred  pounds 
per  acre  will  reduce  the  amount  of  infection. 

BLACKLEG 
Caused  by  Bacillus  phytopthorus  Appel. 

Blackleg  is  a  dangerous  disease  which  may  readily 
be  introduced  into  new  localities  with  the  seed.  The 
trouble  has  been  well  described  by  Morse.1 

Symptoms.  Blackleg  does  not  manifest  itself  until 
the  plants  are  about  7  to  10  inches  high.  Diseased 
plants  are  unthrifty,  undersized,  with  the  branches 

1  Morse,  W.  J.,  Maine  Agr.  Expt.  Sta.  Bui.  174:  307-328,  1909. 


Family  Solanaceae  317 

growing  upward,  forming  a  compact  top.  In  severe 
cases,  affected  plants  turn  yellowish,  topple  over,  and 
die.  On  pulling  out  a  diseased  hill,  we  find  that  the 
stem  end  near  the  seed  potato  is  black  (fig.  59  f). 
This  blackness  may  extend  even  one  or  two  inches  on 
the  stem  above  the  ground.  The  seed  pieces  in  this 
case  soft  rot.  Occasionally  the  newly  formed  tubers 
become  infected  in  the  soil  and  rapidly  soft  rot. 
The  disease  is  carried  in  the  interior  of  the  infected 
seed  tubers,  and  in  this  way  is  distributed  from  one 
locality  to  another.  Blackleg  is  now  prevalent  in 
Maine,  South  Carolina,  Virginia,  Maryland,  Dela- 
ware, New  Jersey,  New  York,  Ohio,  Oregon,  and  possi- 
bly also  in  Florida,  Georgia,  New  Hampshire,  North 
Carolina,  Rhode  Island,  Vermont,  and  Wisconsin. 

The  Organism.  Bacillus  phytopthorus  is  a  rod- 
shaped  organism,  motile  by  means  of  peritrichiate 
flagella.  It  is  an  aerobe,  non-sporiferous,  liquefying 
gelatin  slowly  and  producing  no  gas.  On  agar,  the 
colonies  are  grayish  white,  round,  and  smooth. 

Control.  Careful  selection  of  the  seed  tubers  is 
essential.  Those  which  show  evidence  of  internal 
discoloration  or  rot  should  be  disinfected  with 
formaldehyde,  see  p.  336. 

SOUTHERN  WILT,  see  TOMATO,  p.  342. 

COMMON  SCAB 
Caused  by  Actinomyces  chromo genus  Gasp. 

Common  scab  is  a  disease  which  is  generally  skin 
deep.  The  kind  of  injury  and  the  severity  of  infeo 


3i 8  Diseases  of  Truck  Crops 

tion  depends  on  the  variety  of  tuber  and  the  cultural 
conditions.  Common  scab  may  often  be  confused 
with  powdery  scab;  but  a  careful  examination  will 
reveal  striking  differences. 

Symptoms.  The  disease  attacks  the  tubers  only. 
It  begins  as  small  surface  spots  or  stains,  which  soon 
spread  and  increase  in  depth,  penetrating  to  a  depth 
of  a  half  centimeter.  The  spots  consist  of  accumu- 
lated corky  tissue  which  may  be  readily  removed 
(fig.  59  g).  The  diseased  cells  lose  their  starch  and 
are  filled  instead  with  what  appears  as  fat  globules. 
The  scab  spot  is  merely  the  result  of  the  corky  cam- 
bium cells  which  are  formed  to  protect  the  inner 
starch-bearing  parenchyma  tissue  from  the  irrita- 
tion of  the  parasite.  Scab  does  not  impair  the  germi- 
nation of  the  seed,  but  it  reduces  the  yield  as  well  as 
prejudicing  the  keeping  qualities  of  the  tubers.  It 
does  not  in  any  way  impair  their  edible  quality. 

The  Organism.  The  scab-causing  organism  was 
formerly  believed  to  belong  to  the  class  of  fungi  and 
was  originally  named  Oospora  scabies  Thaxter.  But 
two  American  workers,  Lutman  and  Cunningham,1 
found  that  the  scab  organism  is  not  a  fungus,  but 
belongs  to  the  thread  bacteria  (fig.  59  h,  i).  A. 
chromogenus  consists  of  long  irregular  filaments;  the 
cross  walls  of  the  branches  are  scarcely  visible.  On 
agar,  under  lack  of  moisture  conditions  or  concentra- 
tion of  medium,  the  filaments  grow  out,  and  become 
closely  segmented  into  short  rods  known  as  gonidia 

1  Lutman,  B.  F.,  and  Cunningham,  G.  C.,  Vermont  Agr.  Expt.  Sta. 
Bui.  184  : 3-64,  1914. 


Family  Solanaceae  319 

or  spores.  The  filaments  or  gonidia  are  non-motile. 
It  produces  no  gas,  but  is  capable  of  producing  a 
brown  pigment  which  is  soluble  and  diffuses  through 
the  medium. 

Control.  The  disease  is  carried  about  with  infected 
tubers.  The  latter  when  fed  to  cattle  will  infect  the 
manure.  The  scab  organism  can  pass  the  digestive 
tract  of  the  cows  or  horses  without  losing  its  vitality. 
Before  planting,  seed  potatoes  should  be  disinfected 
with  corrosive  sublimate  or  formaldehyde.  See  also 
p.  336.  Fertilizers  which  tend  to  make  the  soil  alka- 
line, such  as  barnyard  manure,  lime,  wood  ashes,  or 
bone  meal,  all  tend  to  increase  scabby  potatoes.  The 
use  of  kainit,  muriate  of  potash,  sulphur,  or  acid 
phosphate  as  a  fertilizer  all  tend  to  decrease  scab. 

BLACK  WART 

Caused  by  Chrysophylyctis  endobioticum  (Schilb.) 
Perc. 

Black  wart  is  perhaps  one  of  the  most  dangerous  of 
the  potato  diseases.  The  trouble  is  now  prevalent 
in  Germany,  England,  Upper  Hungary,  and  in  New- 
foundland. The  disease  has  not  as  yet  made  its 
appearance  in  the  United  States,  although  it  is 
believed  that  infected  potatoes  have  been  shipped  in 
from  Newfoundland. 

Symptoms.  In  early  stages  of  infection,  the  eyes 
are  first  attacked,  turning  brown  and  later  black. 
The  disease  then  works  down  to  the  tuber,  which 
is  but  slightly  disfigured.  In  advanced  stages,  big 


320  Diseases  of  Truck  Crops 

dark  warts,  sometimes  as  large  as  the  tuber  itself, 
appear  on  its  sides  or  ends  (fig.  61  a).  The  warty 
growth  consists  of  a  scabby  gall-like  formation, 
closely  resembling  the  crown  gall  of  the  peach.  The 
last  stage  of  the  disease  is  when  the  fungus  has  utilized 
all  the  food  stored  in  the  tuber  and  has  reduced  it  to  a 
brownish  black,  soft  mass  with  a  very  offensive  odor. 
At  this  stage  the  fungus  consists  almost  entirely  of  a 
mass  of  spores  which,  when  disturbed,  scatter  and 
spread  all  over  the  field. 

The  Organism.  Chrysophylyctis  endobioticum  has 
been  investigated  by  Johnson1  and  others.  The 
vegetative  parts  of  the  fungus  consist  first  of  a  naked 
mass  of  protoplasm  which  attacks  and  feeds  on  the 
protoplasm  of  the  cells  of  the  host.  As  this  bores 
from  cell  to  cell,  it  stimulates  abnormal  growth,  which 
results  in  the  warts  or  galls  already  mentioned. 
During  the  summer,  the  plasmodium  rounds  up, 
forming  a  thin  smooth  wall  about  itself.  Later  the 
contents  of  this  body  break  up  into  numerous  zoo- 
spores,  which  escape  through  a  hole  in  the  cell  wall 
and  attack  healthy  potato  tissue.  As  the  season 
advances,  the  fungus  ceases  to  reproduce  by  means  of 
zoosporangia  and  zoospores  and  forms  a  resting  spo- 
rangium. This  helps  to  carry  the  fungus  over  the 
winter,  and  the  following  spring  it  germinates  by 
means  of  zoospores. 

Control.  So  far,  there  are  no  methods  of  control 
known.  It  is  imperative  that  we  prevent  black  wart 

Johnson,  T.,  The  Scientific  Proceedings  of  the  Royal  Dublin  Soc., 
Vol.  12,  1909. 


Family  Solanaceae  321 

from  getting  a  foothold  in  the  United  States.  This 
can  be  accomplished  only  by  strict  quarantine  laws 
prohibiting  the  importation  of  tubers  from  countries 
where  wart  is  prevalent. 

MELTERS  OR  LEAK 

Caused  by  Pythium  de  Baryanum  Hesse;  Rhizo- 
pus  nigricans  Ehr. 

Melters  is  a  common  storage  and  shipping  disease. 
The  trouble  is  prevalent  in  the  Delta  region  of  San 
Joaquin  River,  California.  The  rot  is  common 
during  hot  weather  and  begins  to  work  soon  after 
harvesting. 

Symptoms.  The  disease  first  appears  as  small  dis- 
colorations  at  a  cut  or  bruise  made  by  an  im- 
plement at  harvesting.  The  rot  does  not  affect 
unbruised  tubers.  Later  the  affected  potatoes  turn 
brown,  become  soft  (fig.  61  g),  and  if  pressure  is 
applied  a  brownish  watery  liquid  exudes,  wetting  the 
neighboring  tubers. 

The  Organism.  Or  ton1  has  shown  that  leak  may 
be  induced  by  the  fungus  Kkizopus  nigricans.  For 
a  fuller  description  of  this  fungus,  see  soft  rot  of  sweet 
potatoes,  p.  156.  Hawkins2  has  further  shown  that 
leak  may  also  be  caused  by  the  fungus  Pythium  de 
Baryanum.  For  a  description  of  the  latter,  see  also 
damping  off,  p.  43. 

1  Orton,  W.  A.,  U.  S.  Dept.  of  Agr.  Bur.  PI.  Ind.  Circ.  23  : 1 1,  1909. 
3  Hawkins,  L.  A.,  U.  S.  Dept.  Agr.  Jour.  Agr.  Research,  7: 627-639, 
1916. 

81 


322  Diseases  of  Truck  Crops 

LATE  BLIGHT 
Caused  by  Phytophthora  infestans  (Mont.)  De  Bary. 

Late  blight  is  a  disease  which  is  restricted  to  some 
parts  of  the  United  States.  As  it  thrives  best  in 
States  where  the  midsummers  are  moist  and  cool, 
it  is  common  in  the  Northern  States.  Farther 
south  or  west,  it  is  unknown  or  it  occurs  sporadically, 
causing  little  damage. 

Symptoms.  Late  blight  attacks  both  the  foliage 
and  the  tubers  in  the  field,  or  the  tubers  alone  in 
storage,  the  disease  appearing  when  the  plants  have 
passed  the  flowering  stage. 

On  the  leaves  the  trouble  is  first  manifested  as 
purplish  black  or  brownish  black  areas  on  the  lower 
side  (fig.  6 1  b).  It  attracts  attention  only  when  the 
upper  leaves  are  attacked  and  ^blackened.  At  first 
the  infected  leaves  become  watersoaked  and  pale, 
then  they  wilt  and  blacken.  On  examining  an  in- 
fected leaf  during  a  dewy  morning,  a  delicate  growth 
of  the  fungus  is  perceptible  as  a  fine  powdery 
bloom  on  the  under  side. 

When  the  tops  are  badly  blighted,  the  tubers  too 
will  show  evidence  of  disease.  In  early  stages  the 
infection  becomes  perceptible  as  brownish  to  pur- 
plish discoloration  of  the  skin  with  a  softening  of  the 
inner  tissue  (fig.  61  c).  In  dry,  well  drained  soils, 
the  progress  of  the  disease  underground  is  slow,  and 
at  harvesting  dry  rot  may  be  in  evidence.  Infected 
tubers  when  stored  in  cool,  dry  cellars  may  pass  the 


FIG.  61.     POTATO  DISEASES. 

a.  Black  wart  (after  Giissow),  &.  late  blight  on  foliage,  c.  late  blight  on  tuber,  d. 
successive  stages  of  the  development  of  the  conidia  of  Phyiophthora  infestans  (b. 
and  d.  after  L.  R.  Jones),  e.  germination  of  conidia  of  Phyiophihora  infestans,  by 
means  of  zoopores  (after  Ward),/,  mature  oogpnium  of  P.  infestans  (after  Clinton), 
/?.  melters,  surface  view,  early  stage  of  infection,  h.  pycnidium  of  Phoma  tuberosa 
(after  Melhus  and  Rosenbaum). 


Family  Solanaceae  323 

winter  unhurt,  the  rot  being  checked  by  the  favorable 
storage  conditions. 

The  Organism.  The  mycelium  of  the  fungus  is 
hyaline,  non-septate.  As  shown  by  Melhus1  and 
others,  the  mycelium  may  be  carried  from  year  to 
year  within  the  infected  tubers.  In  fact  this  is  but 
one  way  late  blight  is  distributed.  Through  the 
stomata  of  the  infected  leaf  emerge  the  slender  coni- 
diophores  (fig.  51  d),  bearing  the  ovoid  conidia.  Ac- 
cording to  Melhus,  a  the  conidia  of  Phytophthora  infes- 
tans  may  germinate  either  directly  by  a  germ  tube 
or  by  the  production  of  zoospores  (fig.  61  e)  as  in 
Pythium.  The  best  germination  occurs  at  the  op- 
timum temperature,  which  lies  between  10  and  13°  C. 
(50-57°  P.).  The  conidia  may  be  killed  by  exposure 
for  6  to  24  hours  to  dry  atmospheric  conditions  such 
as  exist  in  an  ordinary  room.  Frost  which  kills  the 
top  of  the  plants  will  also  kill  the  conidia  of  Pytho- 
phthora.  Light  does  not  hinder  germination  and 
therefore  has  no  inhibiting  effect  on  infection. 
Phytophthora  infestans  does  not  seem  to  produce  sex- 
ual spores  or  oospores  within  the  affected  tissue  of 
the  leaf  or  tuber.  However,  Clinton3  succeeded  in 
developing  what  appeared  to  be  oospores  of  the 
fungus  in  pure  culture  on  oat  agar  (fig.  61  f).  The 
oogonia  appear  as  swollen  terminal  heads,  cut  off 

1  Melhus,  I.  E.,  U.  S.  Dept.  of  Agr.  Jour.  Agr.  Research,  5  :  59-65, 

15- 

a  Melhus,  I.  E.f  Wisconsin  Agr.  Expt.  Sta.  Research  Bui.  37  :  1-64, 


3  Clinton,  G.  P.,  Connecticut  Agr.  Expt.  Sta.  Ann.  Rept.,  1909- 
1910:753-774. 


324  Diseases  of  Truck  Crops 

from  the  main  thread  by  a  cross  wall.  The  antherid- 
ium  resembles  that  of  P.  phaseoli.  Mature  oospores 
have  a  medium ,  thick,  smooth,  hyaline  wall.  It  is 
not  known  how  the  oospores  germinate.  For  meth- 
ods of  control,  see  p.  337. 

PHOMA  ROT 
Caused  by  Phoma  solani  Mel.,  Rosen.,  and  Sch. 

Phoma  rot  is  found  only  on  bruised  tubers.  It  is 
also  found  following  injuries  produced  by  powdery 
scab,  Spongospora  subterranea.  The  lesions  of  phoma 
rot  are  brownish  dark  to  gray  dark  sunken  pits  with 
irregular  and  sharply  defined  margins.  The  black 
pycnidia  (fig.  61  h)  are  found  scattered  over  the  entire 
surface  of  the  lesions.  The  disease  may  cause  con- 
siderable damage  in  storage.  The  remedy  consists  in 
careful  handling  of  the  tubers  during  digging  and 
storing. 

ANTHRACNOSE 

Caused  by  Colletotrichum  atramentarium  (Berk, 
and  Br.)  Taub.1 

Anthracnose  was  first  described  by  O'Gara2  as 
a  disease  attacking  the  foot  of  the  plant.  The 
fungus  was  originally  named  Colletotrichum  solani- 
colum  O'Gara,  but  was  later  changed  by  the 
writer  to  C.  atramentarium.  It  causes  deep  lesions 

1  Taubenhaus,  J.  J.,  Mem.  N.  Y.  Bot.  Card.,  6  :  549-560, 1916. 

2  O'Gara,  P.  J.,  Mycologia,  7  :  38-41,  1915. 


FIG.  62.    POTATO  DISEASES. 

c.  Early  blight  (after  L.  R.  Jone^),  b.  spores  of  the  early  blight  fungus,  c.  silver 
scurf,  d.  conidiophores  and  conidia  of  the  silver  scurf  fungus,  e.  and  /.  Fusarium 
oxysporum  wilt  in  tubers,  g.  chlamydospores  and  one  to  several  celled  conidia  of 
F.  oxysporum,  h.  conidiophores  of  F.  oxysporum  (g.  and  h.  after  Sherbakoff) ,  *.  Ver- 
ticillium  wilt  (after  Orton). 


Family  Solanaceae  325 

on  the  stems,  usually  attacking  plants  which  are  full 
grown.  It  is  also  found  as  a  saprophyte  in  the  soil, 
or  growing  on  dead  potato  vines;  or  frequently 
associated  with  silver  scurf  on  the  tuber.  It  was 
previously  thought  to  be  a  sclerotial  stage  of 
Spondylocladium  atrovirens  Harz.  Colletotrichum 
atramentarium  differs  from  most  Colletotrichums  in 
that  it  produces  an  abundance  of  sclerotia  both 
on  the  host  and  in  pure  culture.  It  sporulates  very 
poorly  but  otherwise  possesses  all  the  characteristics 
of  the  genus  Colletotrichum. 

EARLY  BLIGHT 
Caused  by  Macrosporium  solani  E.  and  M. 

Early  blight  attacks  the  foliage  only.  Infection 
seems  to  follow  injury  from  insects  such  as  the  potato 
beetle  and  the  flea  beetle. 

Symptoms.  The  disease  is  characterized  by  cir- 
cular or  irregular  brown  dry  spots  made  up  of  a  suc- 
cession of  rings  (fig.  62  a).  The  spots  may  become  so 
numerous  as  to  involve  the  entire  foliage  and  cause 
premature  death  of  the  tops. 

The  Organism.  The  mycelium  is  brownish  to  olive 
in  color.  The  conidiophores  arise  through  the  sto- 
mata  of  the  leaf.  The  conidia  are  produced  singly, 
the  body  of  the  spore  has  from  4  to  12  transverse 
septa,  with  few  longitudinal  cross  walls  (fig.  62  b). 
When  germinating,  a  germ  tube  may  be  produced 
from  each  cell  of  the  conidia.  This  penetrates  the 


326  Diseases  of  Truck  Crops 

leaf  either  through  the  stomata  or  by  piercing  through 
the  cell  wall  of  the  epidermis.  Early  blight  may  be 
controlled  by  spraying,  see  p.  337. 

SILVER  SCURF 
Caused  by  Spondylocladium  atrovirens  Harz. 

Silver  scurf  is  prevalent  throughout  the  East. 
Fortunately  the  disease  does  not  cause  much  direct 
damage,  since  it  is  confined  only  to  the  exterior  of  the 
epidermis.  It  is  claimed  that  affected  tubers  are 
subject  to  more  rapid  shrinking  and  drying.  The 
spots  on  the  tubers  are  brown  and  turn  silvery  when 
moistened  (fig.  62  c). 

The  Organism.  The  conidiophores  are  borne  either 
singly  or  in  clusters,  erect  septate,  with  numerous 
sterigmata  which  bear  the  spores  (fig.  62  d).  The 
conidia  are  thick  walled,  elongate,  many  septate,  apex 
narrowed  and  longer  at  the  bottom. 

Control.  Seed  treatment  does  not  seem  to  control 
the  disease.  Since  silvery  scurf  is  directly  carried 
with  the  seed  tubers,  selection  of  clean  seed  is  recom- 
mended. 

VERTICILLIUM  WILT 

Caused  byVerticillium  albo-atrum  McA. 

Verticillium  wilt  is  not  a  dangerous  disease  when 
compared  with  Fusarium  wilt.  It  does  not  kill  out 


Family  Solanaceae  327 

entire  fields  but  is  generally  confined  to  individual 
hills  irregularly  scattered  in  a  field.  In  distribution, 
Verticillium  wilt  has  been  found  only  in  the  more 
northern  States. 

Symptoms.  The  disease  as  described  by  Orton1  is 
characterized  by  a  sudden  wilting  of  the  foliage  (fig. 
62  i)  and  the  premature  dying  of  the  hill.  In  split- 
ting open  a  diseased  stem,  the  browning  of  the  vessels 
will  be  well  marked.  This  will  extend  to  the  tips  of 
the  stems  and  into  the  leaf  petioles,  a  symptom  which 
distinguishes  it  from  Fusarium  wilt,  since  in  the  latter 
the  browning  of  the  vessels  does  not  extend  into  the 
tips  of  the  stalks.  Moreover,  in  Verticillium  wilt 
there  is  a  production  of  conidia  on  the  stalks  long 
before  they  are  entirely  dead.  In  Fusarium  wilt, 
the  conidia  appear  only  after  the  stem  has  been  killed 
for  some  time. 

Control.  Since  the  disease  is  carried  internally  in 
the  seed  tubers,  control  methods  are  the  same  as  for 
Fusarium  wilt. 

FUSARIUM  WILT 
Caused  by  Fusarium  oxysporum  (Sch.)  Sm.  and  Sw. 

Fusarium  wilt  is  a  disease  which  thrives  best  in 
warm  climates.  In  California,  Arizona,  Ohio,  Mis- 
souri, and  Nebraska  the  trouble  is  most  prevalent. 
New  England  and  New  York  are  relatively  free  from 
Fusarium  wilt.  There,  however,  the  Verticillium 

1  Orton,  W.  A.,  U.  S.  Dept.  of  Agr.  Bui.  64  : 16-18,  1914. 


328  Diseases  of  Truck  Crops 

wilt  is  prevalent.  In  Michigan,  Illinois,  Wisconsin, 
and  Minnesota,  Fusarium  wilt  is  found  in  the  older 
potato  districts.  The  trouble  is  also  found  in  Colo- 
rado and  Utah  where  it  thrives  on  irrigated  as  well  as 
on  dry  lands,  on  sandy  loams  as  well  as  on  the  heavier 
clays. 

Symptoms.  When  infected  seeds  are  planted,  the 
result  is  a  poor  germination  and  uneven  stand.  The 
disease  however  does  not  attract  attention  until  the 
plant  attains  a  height  of  a  foot  or  more. 

Wilt  is  characterized  by  a  drooping  of  the  lower 
leaves,  which  are  first  to  die.  This  is  followed  by  a 
wilting  of  the  upper  foliage  and  by  a  premature  dying 
of  the  tops.  The  leaf  roll  that  is  noticed  in  Fusarium 
wilt  differs  from  true  leaf  roll  in  that  in  the  former 
the  leaves  lack  the  turgidity  and  soon  die  as  a  result 
of  the  infection .  Wilted  plants  are  at  first  light  green , 
then  yellow,  finally  drying  up  and  dying.  The  disease 
first  gains  entrance  through  the  tender  rootlets  in  the 
soil,  gradually  working  up  into  the  main  roots,  stolons, 
tubers  (fig.  62  e,  f),  and  some  way  into  the  stem.  In 
splitting  open  a  diseased  stem,  the  interior  water 
vessels  are  found  to  be  slightly  browned.  But  few 
Fusarium  spores  are  formed  on  the  dead  stems.  In 
the  tubers  the  presence  of  wilt  is  indicated  by  a 
browning  of  the  vascular  rings. 

The  Organism.  The  microconidia  are  pedicellate, 
sporodochia  and  pseudopionnotes  present,  macro- 
conidia  4  to  5  septate,  pinkish  buff  color  in  mass 
(fig.  62  g,  h).  Bluish  black  sclerotia  are  formed  on 
potato  plugs.  For  methods  of  control  see  p.  337. 


Family  Solanaceas  329 

BLACK  ROT  OR  JELLY  END  ROT 
Caused  by  Fusarium  radicicola  Woll. 

This  disease  is  seldom  found  in  the  field  at  digging 
but  is  usually  manifested  as  a  storage  trouble.  It  is 
common  in  Idaho,  Oregon,  Washington,  California, 
Nevada,  Mississippi,  New  York,  Virginia,  District 
of  Columbia,  and  certain  parts  of  Pennsylvania. 

Symptoms.  In  the  irrigated  sections  of  California, 
Oregon,  and  Idaho  the  trouble  is  manifested  as  a  soft 
rot  termed  " Jelly  End  Rot."  The  stem  end  soft 
rots,  and  the  affected  portion  may  be  easily  removed 
from  the  remainder  of  the  tuber.  The  disease  pro- 
gresses inwards  until  the  entire  tuber  within  the  skin 
becomes  soft  and  jelly  like  in  consistency.  If  not 
disturbed,  the  inside  tissue  will  dry,  and  the  skin  per- 
sist as  a  loose  tunic,  or  it  may  shrivel  and  shrink, 
giving  the  appearance  of  a  dry  rot. 

In  the  non-irrigated  potato  districts,  the  symptoms 
of  the  disease  are  sunken,  blackish,  leathery  areas  on 
any  part  of  the  tubers.  In  Pennsylvania  the  disease 
is  known  as  "black  rot"  or  "black  head.'*  Micro- 
conidia  of  the  fungus  are  the  dominant  type  of 
spores.  Chlamydospores  are  common  and  pseudo- 
pionnotes  are  absent,  while  sporodochia  are  usually 
present. 

Control.  This  disease  does  not  make  any  progress 
in  storage  at  or  below  fifty  degrees  F.  The  trouble 
is  confined  mostly  to  the  Idaho,  Rural,  and  Pearl. 
So  far  as  possible,  these  should  be  avoided  and  re- 


330  Diseases  of  Truck  Crops 

placed  by  the  more  resistant  varieties  best  adapted  to 
the  infected  localities. 

STEM  END  ROT 
Caused  by  Fusarium  eumartii  Carp. 

Although  a  storage  trouble,  stem  end  rot  may  cause 
a  wilt  in  the  field  which  may  not  be  easily  distin- 
guished from  other  Fusarium  wilts.  However,  in 
the  laboratory  the  causative  organism  may  be  readily 
determined  by  pure  culture  methods. 

Symptoms.  The  wilt  produced  on  plants  in  the 
field  resembles  other  wilts.  On  the  tubers,  decay 
starts  at  the  stem  end.  The  infected  part  slowly 
shrivels  and  becomes  filled  with  a  mass  of  a  dried 
brown  pulp,  consisting  mainly  of  dead  tissue.  In- 
fection usually  takes  place  through  a  wound  or  even 
through  a  lenticel  in  the  tuber.  The  fungus  is  char- 
acterized by  its  production  of  macroconidia  which  are 
4  to  6  septate,  pionnotes  are  present,  otherwise  the 
organism  resembles  F.  martii. 

For  control,  see  p.  337. 

POWDERY  DRY  ROT 
Caused  by  Fusarium  trichoihecioides  Woll. 

Powdery  dry  rot  is  a  storage  trouble  which  is  pre- 
valent in  the  arid  and  semi-arid  sections  of  the 
western  part  of  the  United  States.  The  disease  was 


FIG.  63.     POTATO  DISEASES. 

a.  Powdery  dry  rot,  b.  Rhizoctonia  lesion  on  young  potato  sprouts  (after  W.  A. 
Orton),  c.  Rhizoctonia  sclerotia  on  seed  potato  tubers,  d.  melters,  artificially  in- 
duced by  inoculating  with  a  pure  culture  of  Sclerotium  Roljsii.  e.  pure  culture  of 
5.  Rolfsii. 


Family  Solanaceae  331 

first  described  by  Jamieson  and  Wollenweber. x  The 
trouble  is  the  same  as  that  described  by  Wilcox2 
and  the  causative  organism  was  previously  named 
Fusarium  tuberivorum.  In  poorly  ventilated  storage 
houses,  bruised  potatoes  dry  rot  (fig.  63  a),  the  entire 
content  of  the  tuber  turning  into  a  powdery  mass. 
The  disease  does  not  attack  growing  plants  in  the 
field  nor  unbruised  tubers. 

There  are  numerous  other  species  of  Fusaria  which 
are  capable  of  producing  a  rot  on  tubers  through  a 
wound.  Sherbakoff3  mentions  twenty-eight  of  them 
which  may  produce  a  rot  on  stored  potatoes. 

ROSETTE  OR  RUSSET  SCAB 

Caused  by  Corticium  vagum  B.  and  C.  var.  solani 
Burt. 

Rosette,  although  generally  distributed,  is  more 
prevalent  in  the  Eastern  States.  The  disease  is 
often  very  serious,  and  causes  great  money  losses. 
The  trouble  attacks  the  tuber  as  well  as  the  foot  of 
the  stem. 

Symptoms.  On  the  tubers  the  disease  is  recognized 
as  superficial  dark  brown  sclerotia  varying  in  size  from 
that  of  a  mustard  seed  to  that  of  a  vetch  (fig.  630). 

1  Jamieson,  C.  O.,  and  Wollenweber,  H.  W.,  Jour.  Wash.  Acad. 
Sci.,  2  :  146-152,  1912. 

2  Wilcox,  E.  M.,  et  al.,  Nebraska  Agr.  Expt.  Sta.  Research  Bui. 
I  :  1-88,  1913. 

3  Sherbakoff,  C.  D.,  New  York  (Ithaca)  Agr.  Expt.  Sta.  Mem., 
6:97-270,  1915- 


332  Diseases  of  Truck  Crops 

In  planting  infected  tubers,  the  sclerotia  germinate 
and  the  growing  fungus  threads  attack  the  young 
sprouts,  causing  lesions  (fig.  63  b).  These  may  be 
superficial  or  so  deep  as  almost  to  girdle  the  stems. 
The  lesions  are  usually  numerous.  Infected  plants 
attempt  to  overcome  the  ill  effect  of  the  disease  by 
sending  out  numerous  sprouts  above  the  injured 
parts,  giving  the  appearance  of  a  rosette.  Diseased 
hills  often  produce  aerial  tubers.  The  disease  is 
spread  about  by  the  use  of  the  infected  seed  tubers. 
The  causative  fungus,  once  introduced  into  a  field, 
will  live  in  the  soil  on  dead  organic  matter  and  attack 
numerous  other  crops.  Rosette  is  worse  on  wet, 
poorly  drained  soils,  and  during  seasons  of  heavy 
rainfall.  Recently  Rosenbaum x  has  found  that  there 
are  variations  in  the  strains  of  Rhizoctonia  isolated 
from  diseased  potatoes.  Some  of  the  strains  seem  to 
be  more  virulent  pathologically,  and  differ  morpho- 
logically from  others.  For  methods  of  control,  see 

P-  336. 
SOUTHERN  BLIGHT  (fig.  63  d-e),  see  PEPPER  p.  305. 

ROOT  KNOT 
Caused  by  Heterodera  radicicola  (Greef)  Muller. 

Root  knot  on  the  potato  may  be  easily  overlooked. 
Usually  there  are  no  knots  on  the  tubers,  and  the 
trouble  is  merely  manifested  by  minute  pimples  on 
the  surface  of  the  potato,  resembling  the  pimples 

1  Rosenbaum,  J.,  U.  S.  Dept.  of  Agr.,  Jour.  Agr.  Research,  9  : 413- 
419,  1917. 


Family  Solanacese  333 

induced  by  flea  beetle  injury.  Small  knots  resem- 
bling legume  nodules  may  occasionally  be  formed  on 
the  smaller  rootlets  of  the  plant.  For  a  further  de- 
scription of  root  knot,  see  Nematode,  p.  49. 

CONTROL  OF  POTATO  STORAGE  ROTS 

As  seen  above,  numerous  fungi  are  capable  of  pro- 
ducing a  rot  on  bruised  potatoes.  The  greatest  loss 
from  this  source  occurs  when  the  tubers  are  held  in 
storage.  Most  of  this  loss,  however,  could  be  reduced 
to  a  minimum  if  more  care  were  exercised  at  digging. 
Few  realized  the  heavy  losses  from  bruises  and  cuts 
and  rough  handling  in  the  field.  This  could  be  best 
appreciated  if  we  were  to  watch  the  storers  sort  out 
the  tubers,  to  prepare  them  for  the  market.  A  visit 
to  the  retail  stores  where  quantities  of  unsalable 
potatoes  are  dumped  out  will  also  convince  us  why 
the  grower  must  exercise  more  care. 

Potatoes  are  usually  stored  in  pits,  in  cellars  or 
dug-outs,  and  in  insulated  frame  structures.  In  the 
larger  storage  houses,  conditions  may  be  better  regu- 
lated than  in  pits  or  cellars.  No  matter  which 
method  of  storage  we  adopt,  there  are  certain 
fundamental  principles  to  observe. 

Temperature.  Upon  proper  temperature  usually 
depends  success  in  storing.  Careful  investigations 
by  the  United  States  Department  of  Agriculture  has 
shown  that  the  freezing  point  of  Irish  potatoes  lies 
between  26  and  28  degrees  F.  This  means  that  po- 
tatoes can  stand  the  low  temperatures,  which  are 


334  Diseases  of  Truck  Crops 

especially  necessary  for  good  keeping.  A  tempera- 
ture of  about  thirty-six  degrees  F.  may  be  considered 
ideal  for  the  best  keeping.  This  temperature  will 
keep  the  tubers  in  the  best  of  condition  and  will  also 
inhibit  the  work  of  decay  organisms.  It  is  claimed 
that  when  potatoes  are  stored  at  low  temperatures 
they  take  on  a  sweetish  taste  when  cooked.  This 
may  or  may  not  be  an  objectionable  feature.  This 
objection,  however,  is  of  little  significance,  when  we 
consider  the  fact  that  stored  potatoes  become  normal 
in  taste  after  being  kept  a  week  at  the  retailer's 
store  at  ordinary  room  temperature. 

Moisture.  Little  is  known  as  to  the  amount  of 
moisture  necessary  during  potato  storage.  The 
object,  however,  should  be  to  maintain  sufficient 
moisture  in  the  air  to  prevent  excessive  drying  of  the 
tubers,  and  at  the  same  time  to  keep  the  moisture 
content  low  enough  to  prevent  it  from  condensing  and 
falling  on  the  potatoes.  Appleman1  suggests  that 
storage  houses  be  maintained  at  33  to  35  degrees  F., 
and  at  a  humidity  of  85  to  90  per  cent. 

Ventilation.  Pure  fresh  air  seems  to  be  necessary 
to  insure  successful  storage.  This  may  be  secured 
by  top  and  side  ventilators  installed  in  the  storage 
house.  In  pit  or  cellar  storage,  neither  the  tem- 
perature nor  the  relative  humidity  can  be  suc- 
cessfully controlled.  Here  the  trucker  is  entirely 
dependent  on  the  chances  of  natural  weather  con- 
ditions. 

Bins.     It  is  bad  practice  to  store  in  large  bins  or 

1  Appleman,  C.  O.,  Maryland  Agr.  Expt.  Sta.  Bui.  167 : 330, 1912. 


Family  Solanaceae  335 

piles,  for  the  potatoes  in  them  are  almost  certain  to 
undergo  a  heat  which  will  destroy  their  keeping  and 
germinating  power.  This  is  a  serious  matter  in  stor- 
ing seed  potatoes.  Bins  should  be  small,  provided 
with  a  false  floor,  and  separated  one  from  the  other 
by  a  two-inch  air  space.  Direct  sunlight  should  be 
kept  from  the  storage.  Subdued  light  or  electricity 
will  not  cause  the  tubers  to  turn  green  and  unfit  for 
cooking.  Finally,  only  sound  tubers  should  be  stored. 
The  storage  house  should  be  carefully  cleaned  out 
before  the  crop  is  brought  in  from  the  field  and  the 
interior  walls  and  woodwork  thoroughly  disinfected 
by  burning  flowers  of  sulphur. 

Care  in  Shipping.  In  Florida  potatoes  are  shipped 
in  double-headed  barrels,  as  is  done  for  apples.  No 
matter  in  what  receptacles  potatoes  are  shipped,  it 
is  imperative  to  avoid  rough  handling  and  to  pack 
securely.  This  will  prevent  shaking  and  bruising  of 
the  tubers  while  in  transit.  The  cars  should  be 
cleaned  and  protected  from  leakage.  During  ex- 
treme cold  weather,  the  cars  should  be  generously 
supplied  with  a  layer  of  straw  at  the  bottom  and  at 
the  sides. 

CONTROL  OF  POTATO  DISEASES  IN  THE  FIELD 

It  is  fortunate  that  most  of  the  potato  troubles  in 
the  field  may  be  kept  in  check.  Truckers,  therefore, 
are  no  longer  justified  in  allowing  their  potato  crops 
to  be  carried  off  by  disease. 

Seed  Selection.     Most  of  the  potato  diseases  are 


336  Diseases  of  Truck  Crops 

carried  over  with  the  seed.  The  importance  of  clean, 
carefully  selected  seed  cannot  be  too  strongly  em- 
phasized. Selecting  seed  from  resistant  and  highest 
yielding  hills  is  preferable  to  selecting  from  the  bin. 
In  cutting  the  tuber  into  pieces  for  planting,  none 
should  be  used  that  show  the  least  blemish  or  rot 
on  the  outside,  or  decay  or  discoloration  within. 
By  observing  this  precaution  carefully,  we  shall 
prevent  our  seed  from  carrying  scab,  rosette,  and 
many  of  the  blights  and  wilts.  Selected  clean  seed 
alone  will  not  give  the  desired  result  if  it  is  planted 
on  infected  soil.  Less  disease  may  be  expected 
when  clean  seed  is  planted  on  lands  rotated  with 
alfalfa  or  grain,  than  when  it  is  planted  on  virgin 
land. 

Seed  Disinfection.  The  object  of  disinfecting  seed 
is  to  destroy  disease-producing  organisms  which  may 
be  adhering  to  the  exterior  of  the  seed  coat.  After 
the  seed  pieces  are  cut,  they  should  be  soaked  for  one 
and  a  half  hours  in  a  solution  made  up  of  four  ounces 
of  corrosive  sublimate  dissolved  in  thirty  gallons  of 
water.  It  is  desirable  to  disinfect  the  seed  immedi- 
ately before  planting.  Doing  it  a  week  to  ten  days 
before  planting  leaves  the  risk  of  the  seed  undergo- 
ing heat  and  having  its  germination  injured.  For 
disinfecting  large  quantities  of  seed,  the  dipping 
process  is  too  tedious,  and  a  preferable  method  is 
that  of  the  formaldehyde  gas:  This  method  re- 
quires care,  or  else  we  are  apt  to  injure  the  seed 
badly.  In  this  case,  it  is  essential  to  have  167 
bushels  of  potatoes  for  each  one  thousand  cubic  feet 


Family  Solanaceae  337 

of  space  in  the  disinfecting  room.  With  less  quan- 
tities of  potatoes  in  this  space,  the  formaldehyde 
gas  will  injure  the  germination  and  produce  a  pitting 
on  the  tuber.  A  tight  room  is  used  for  this  purpose, 
and  the  seed  potatoes  are  placed  in  open  crates,  or  in 
layers  in  slated  bins,  or  in  small  piles  on  the  floor. 
For  each  one  thousand  cubic  feet  of  space,  three 
pints  of  formaldehyde  (40%)  pure  and  twenty-three 
ounces  of  potassium  permanganate  should  be  used. 
The  latter  is  placed  in  deep  wooden  or  earthen  dishes, 
and  the  formaldehyde  is  poured  on  the  salt  crystals, 
the  disinfector  rushing  out  locking  the  door  at  once. 
The  fumigated  house  is  kept  closed  for  twenty-four 
hours. 

Spraying.  The  field  diseases  such  as  early  and  late 
blight,  tip  burn,  and,  in  fact,  all  other  foliage  diseases 
except  leaf  roll  and  curly  dwarf  may  be  controlled  by 
spraying.  Lime  sulphur  in  any  form  has  failed  to 
give  satisfactory  results.  The  spray  recommended 
is  5-5-50  Bordeaux  mixture.  To  each  one  hundred 
gallons  of  Bordeaux,  add  one  pound  of  Paris  green 
or  six  pounds  of  lead  arsenate  paste.  Spraying 
should  begin  when  the  plants  are  about  six  inches 
high,  and  from  3  to  6  applications  should  be  given, 
depending  on  the  climatic  conditions.  To  yield  the 
desired  result,  spraying  must  be  applied  in  a  thorough 
manner.  It  is  a  good  form  of  insurance,  as  has  been 
demonstrated  by  many  workers.  Table  16  by  Lut- 
man1  clearly  shows  the  profits  to  be  derived  from 
spraying. 

1  Lutman,  B.  F.,Vennont  Agr.  Expt.  Sta.  Bui.  159 :  216, 296, 1911. 


Diseases  of  Truck  Crops 
TABLE  16 


Gains  from  the  Use  of  Bordeaux  Mixture  on  Late  Potatoes.    20  Years' 

Experiments. 


Yield  per 

Acre 

Variety 

Gain 

Prevalence 

and  Date 

Sprayed 

Per 

of  Late 

of  Planting 

Nnt 

Acre 

Blight 

Sprayed 

IV  (/*• 

Sprayed 

White  Star 

bu. 

bu. 

bu.    % 

May,  1891 

Aug.  26,  Sept.  8 

313 

248 

65     26 

some 

May,  1893 

Aug.  i,  1  6,  29 

291 

99 

192   194 

much 

May  20,  1893 

Aug.  i,  16,  29 

338 

114 

224  196 

much 

Apr.  26,  1894 
May  20,  1895 

June  16,  July  17,  Aug.  30 
July  25,  Aug.  13,  31 

323 

389 

251 
219 

72     29 
170     78 

none 
rot 

Polaris 

May  15,  1896 

Aug.  7,  21 

325 

267 

68     26 

none 

June  i,  1897 
White  Star 

July  27,  Aug.  17,  28 

151 

80 

71     89 

some 

May  10,  1898 

July  21,  Aug.  10 

238 

112 

126    112 

little 

Average  (3  varie- 

ties) 

May  1  8,  1899 

July  26,  Aug.  17,  Sept.  8 

229 

161 

68     42 

little 

Delaware 

May  23,  1900 

Aug.  4,  23 

285 

225 

60     27 

rot 

May  25,  1901 

July  20,  Aug.  21 

170 

54 

116  215 

much 

May  15,  1902 

Aug.  I,  20 

298 

164 

134     82 

severe 

Green  Mountain 

May  i,  1963 

Aug.  10 

36i 

237 

124     52 

severe 

Delaware 

May  25,  1904 

Aug.  i,  Sept.  i 

327 

193 

134     69 

some 

May  15,  1905 

Aug.  2,  21 

382 

221 

161     73 

severe 

Green  Mountain 

May  27,  1906 
May  i,  1907 

Aug.  13,  22 
July  16,  25,  Aug.  8,  22 

133 
171 

IOI 

63 

32     32 
108  175 

some 
little 

May  15,  1908 

June  26,  July  9,  Aug.  6,  26 

156 

65 

91   140 

none 

May  28,  1909 

July  12,  23,  Aug.  6,  27 

243 

188 

55     29 

none 

May  9,  1910 

July  1  1,  27,  Aug.  15,23,3° 

240 

202 

38     18 

none 

Average  for  20  years 

268 

163 

105     64 

Family  Solanaceae  339 

DISEASES  OF  THE  TOMATO  (Lycopersicum 

esculentum) 

Like  potatoes,  tomatoes  are  subject  to  numerous 
diseases  which  the  trucker  cannot  afford  to  ignore  if 
he  is  to  reap  the  greatest  profits  from  his  crop. 

HOLLOW  STEM 
Cause  Physiological. 

Hollow  stem  is  a  trouble  manifested  on  seedlings  in 
the  bed,  or  after  transplanting.  The  central  portion 
of  the  head  of  the  plant  remains  green  while  the  lower 
leaves  turn  yellow.  In  severe  cases,  affected  plants 
fall  over  as  in  damping  off,  with  the  absence,  however, 
of  signs  of  rotting.  Such  plants  when  examined  are 
found  to  have  hollow  stems  and  seem  too  weak  to 
stand  up. 

Cause.  There  are  several  causes,  all  of  which 
when  combined  may  lead  up  to  the  hollow  stem. 
i.  A  highly  nitrogenous  fertilizer  applied  to  the 
seed  bed  to  force  the  seedlings.  2.  An  abundance 
of  water  supply  to  make  the  fertilizer  quickly  avail- 
able. 3.  Sowing  seeds  of  a  rapid  growing  variety. 
4.  Transplanting  without  hardening  off.  5.  Trans- 
planting into  a  dry  soil. 

Control.  It  is  evident  from  what  has  been  said 
that  the  fertilizer  in  the  seed  bed  should  be  well  bal- 
anced. Care  should  be  taken  to  prevent  the  seedling 
from  becoming  leggy,  and  to  see  that  they  are  pro- 
perly hardened  before  transplanting.  The  Stone  and 
its  related  varieties  seem  to  be  more  resistant  to  hollow 


340  Diseases  of  Truck  Crops 

stem.     On  the  other  hand,   the  Dwarf  Champion 
seems  to  be  especially  susceptible  to  hollow  stem. 

BLOSSOM  END  ROT 

Cause  Unknown. 

Blossom  end  rot,  also  known  as  point  end  rot,  may 
be  found  wherever  tomatoes  are  grown.  It  is  a  dis- 
ease of  the  fruit  only.  In  some  seasons  fifty  per  cent. 
or  more  of  the  fruit  crop  is  ruined  by  it.  It  seems 
to  be  more  serious  in  dry  weather  and  on  light  soils. 

Symptoms.  Infection  is  manifested  as  a  water- 
soaked  spot  at  the  blossom  end  of  the  fruit  (fig.  64 
b-c) .  The  size  of  the  spot  may  be  that  of  a  pin-head, 
or  it  may  spread  so  rapidly  as  to  involve  half  of  the 
tomato.  A  few  days  later,  the  water-soaked  spot 
becomes  black  and  leathery  and  ceases  to  make  fur- 
ther progress.  Complete  rotting  of  the  fruit  may  be 
brought  about  by  secondary  invasions. 

Plants  subject  to  frequent  slight  wilting  produce  a 
greater  number  of  defective  fruits.  There  seems  no 
doubt  but  that  the  water  supply  in  the  soil  is  an 
important  factor  in  limiting  or  increasing  blossom  end 
rot.  The  factors  of  drainage  and  cultivation  are 
therefore  important  considerations.  Although  dry 
soils  and  drought  favor  the  increase  of  the  disease,  yet 
the  condition  of  health  of  the  plant  itself  seems  more 
important  than  the  decrease  of  water  supply. 

The  use  of  fertilizers,  too,  seems  to  influence  the 
trouble.  Heavy  applications  of  manure  or  of  potash 
seem  to  increase  the  rot,  as  do  fertilizers  in  the  form  of 


FIG.  64.    TOMATO  DISEASES. 

a.  Various  stages  of  mosaic  on  foliage,  b.  c.  blossom  end  rot,  d.  downy  mildew, 
Phytophthora  infestans,  e.  conidia  of  buck-eye  rot  Phytophthora  terrestris,  f.  conidia 
of  P.  terrestris,  germinating  by  means  of  zoospores,  g.  zoospores,  h.  mature  oospores 
of  P.  terrestris,  i.  buck-eye  rot  (e.  to  i.  after  Sherbakoff). 


Family  Solanaceae  341 

ammonium  compounds.  This  is  especially  true  on 
sandy  loams.  On  the  other  hand,  nitrate  of  soda  or 
lime  seems  to  check  blossom  end  rot. 

SUNBURN 

Tomato  fruits  are  often  burned  while  they  are  on 
the  vines  by  strong  sunlight  beating  on  the  exposed 
fruit.  This  results  in  a  scalding  of  certain  parts  (fig. 
67  e),  loss  of  color,  and  a  local  drying  which  produces 
white  spots  with  a  dry  peppery  appearance.  Such 
fruit  is  unfit  for  the  market.  Sunburn  may  also 
result  from  other  and  indirect  causes.  In  dry  sea- 
sons the  tomato  cannot  supply  the  necessary  supply 
of  moisture  to  the  foliage  and  fruit.  As  a  result,  they 
become  weakened  and  contain  numerous  starved 
areas  which  dry  up  when  exposed  to  strong  sunlight. 
The  same  result  may  also  be  brought  about  by  the  in- 
direct action  of  the  numerous  leaf  and  root  diseases. 

Control.  In  sections  where  sunburn  is  prevalent, 
it  is  advisable  to  plant  tomato  varieties  with  dense 
foliage.  The  plants  should  be  put  out  as  early  as 
possible  so  that  the  vines  may  attain  their  maximum 
before  hot  weather  sets  in.  The  soil  should  be  prop- 
erly fertilized,  and  sufficient  humus  incorporated  to 
hold  the  moisture  during  periods  of  high  temperatures. 
Irrigation  should  be  practiced  wherever  possible. 

MOSAIC 

Cause  Unknown. 

A  lengthy  discussion  on  mosaic  has  already  been 
given  on  p.  83.  Mosaic  on  tomato  is  a  common  field 


342  Diseases  of  Truck  Crops 

trouble,  conspicuous  on  stalks,  fruit,  and  leaves.  On 
the  leaves  it  is  manifested  as  a  mottling  of  yellow 
areas  on  the  tissue  between  the  veins.  The  unequal 
growth  of  tissue  causes  the  leaves  to  warp  and  grow 
unevenly.  In  severe  cases  the  normal  leaflets  are 
replaced  by  a  filform  or  fern-like  structure  (fig.  64  a), 
with  a  striking  dissected  form.  The  blossom  of  the 
diseased  plant  usually  drops  off,  and  the  few  setting 
fruits  are  small  and  deformed. 

SOUTHERN  WILT 
Caused  by  Pseudomonas  solanacearum  Ew.  Sm. 

Southern  wilt  has  a  wide  distribution.  As  its 
name  indicates,  it  is  generally  found  in  the  more 
southern  States.  It  is  generally  severe  in  Texas, 
Alabama,  Georgia,  Mississippi,  North  and  South 
Carolina,  Florida,  Maryland,  Virginia,  New  York, 
and  Connecticut. 

Symptoms.  Infected  plants  usually  wilt  rapidly 
without  losing  their  green  color.  In  large  leaves,  the 
main  axis  is  bent  downward  in  a  drooping  way. 
With  the  young  plants  the  stems  and  foliage  also 
droop  and  shrivel.  The  vascular  system  of  such 
plants  is  browned,  indicating  the  presence  of  the 
causative  organism  within.  In  cutting  across  a 
freshly  wilted  stem,  a  dirty  white  to  brownish  white 
slime  that  is  not  sticky  is  seen  to  ooze  out.  In  soft 
and  rapidly  growing  plants,  the  whole  pith  is  often 
converted  into  a  watery  slime.  In  tomato  and  egg- 
plants the  disease  seldom  attacks  the  fruit  but  is 


Family  Solanaceae  343 

localized  to  the  vegetative  parts.  With  the  Irish 
potato,  the  disease  works  underground  where  it  also 
penetrates  the  tubers.  These  show  a  yellowing  and 
blackening  of  the  veins,  finally  giving  way  to  a  soft 
rot.  On  squeezing,  a  creamy  exudate  oozes  out  from 
the  diseased  veins. 

Southern  wilt  attacks  not  only  the  tomato,  potato, 
and  eggplant,  but  it  also  causes  a  serious  disease  on 
the  tobacco,  peanut,  nasturtium,  ragweed,  im- 
patience, verbena, — plants  which  belong  to  families 
other  than  the  Solanaceae. 

The  Organism.  Pseudomonas  solanacearum  is  a 
medium-sized  rod,  with  rounded  ends  and  motile 
by  means  of  polar  flagella.  Pseudo-zoogloese  are 
common  in  old  cultures.  No  spores  are  formed; 
on  agaragar,  colonies  are  white,  then  dirty  white, 
afterwards  becoming  brown  with  age.  The  or- 
ganism does  not  liquefy  gelatin  and  produces  no 
gas. 

Control.  Crop  rotation  is  the  safest  method  of  con- 
trol. All  crops  subject  to  wilt,  such  as  potato  and 
eggplant  should  be  left  out  from  the  rotation 
system. 

DAMPING  OFF,  see  PYTHIUM,  p.  43. 

LATE  BLIGHT 
Caused  by  Phytophthora  infestans  (Mont.)  De  By. 

Late  blight  usually  attacks  the  fall  tomato  crop. 
It  is  especially  prevalent  during  rainy  weather,  where 
it  may  even  be  found  in  the  seed  bed.  The  trouble 


344  Diseases  of  Truck  Crops 

may  be  found  wherever  Irish  potatoes  are  known  to 
suffer  from  late  blight,  since  the  tomato  and  potato 
blight  are  caused  by  the  same  fungus. 

Symptoms.  Affected  plants  appear  as  though 
killed  by  frost.  The  disease  first  shows  itself  as  small 
blackened  areas  on  the  leaves  (fig.  64  d),  stems,  and 
fruits.  These  rapidly  increase  in  size  and  cause  pre- 
mature death  of  the  affected  host.  Fruits  which  may 
not  show  signs  of  disease  will  develop  the  trouble  in 
transit  if  coming  from  infected  fields.  For  a  de- 
scription of  the  causative  fungus,  see  late  blight  of 
potato,  p.  322.  Late  blight  of  tomatoes  may  be  con- 
trolled by  spraying.  The  best  results  are  obtained 
by  using  5-5-50  Bordeaux.  Spraying  should  begin 
with  the  rainy  season.  The  ripe  fruit  should  be 
cleaned  by  wiping  off  the  Bordeaux  stains  with  a 
dry  cloth. 

BUCKEYE  ROT 
Caused  by  Phytophthora  terrestria  Sherb. 

Buckeye  rot  is  a  disease  which  attacks  the  fruit. 
The  trouble  seems  to  be  new  and  has  been  recently 
described  by  Sherbakoff.1  So  far  as  is  known  the 
disease  has  appeared  only  in  Florida. 

Symptoms.  The  disease,  as  the  name  indicates, 
appears  as  a  pale  to  dark  greenish-brown  zonate  spots 
on  the  fruit  (fig.  64  i) .  The  rot  is  hard  and  somewhat 
dry  when  the  fruit  is  green,  but  becomes  softer  as  the 

1  Sherbakoff,  C.  D.,  Phytopath.  7  :  119-129,  1917. 


Family  Solanaceae  345 

tomato  ripens.  It  usually  begins  at  a  point  where  the 
fruit  touches  the  ground,  which  is  most  commonly 
at  the  blossom  end,  and  might  be  mistaken  for 
blossom  end  rot  were  it  not  for  the  characteristic 
zonations. 

The  Organisms.  The  mycelium  is  at  first  continu- 
ous, then  septate.  Conidia  (fig.  64  e-g)  germinate  by 
means  of  swarm  spores.  Chlamydospores  are  com- 
mon, oospores  (fig.  64  h)  common  on  cornmeal  agar. 
Besides  tomato  fruit,  P.  terrestria  causes  a  foot  rot  of 
citrus  trees  and  a  stem  rot  of  lupines. 

Control.  Tomato  plants,  as  far  as  possible,  should 
be  staked.  By  preventing  the  fruit  from  coming 
into  direct  contact  with  the  soil,  infection  will  be 
avoided.  Fruit  destined  for  distant  markets  should 
not  be  packed  as  soon  as  it  is,  brought  in  from  the 
iield.  If  possible  it  should  be  kept  a  few  days  to 
allow  for  possible  rot  to  develop  so  that  the  affected 
ones  may  be  culled  out  and  destroyed. 

YEAST  ROT 
Caused  by  Nematospora  lycopersici  Sch. 

Yeast  rot,  as  the  name  indicates,  is  induced  by  a 
parasitic  yeast.  This  little  known  trouble  has  been 
investigated  by  Schneider. x 

Symptoms.  The  disease  is  indicated  by  a  slightly 
depressed  reddish-brown  spot.  The  epidermal  area 
of  the  affected  spot  becomes  indurated  and  shriveled. 

Schneider,  A.,  Phytopath.  6  1395-399,  1916;  and  in  Phytopath. 
7  : 52-53, 


346  Diseases  of  Truck  Crops 

The  greatest  amount  of  rotting  occurs  within  the 
fruit. 

The  Organism.  The  parasite  is  a  typical  yeast. 
It  produces  arthrospores  of  non-gametic  origin,  asci 
of  gametic  origin  (fig.  65  a-c).  The  ascospores  are 
formed  in  two  groups  of  four  each,  slender,  one- 
septate,  and  each  containing  a  motionless  flagellum. 
Little  is  known  about  the  control  of  this  disease. 

FRUIT  ROT 
Caused  by  Phoma  destructives  Plowr. 

Fruit  rot  is  found  in  Cuba,  Florida,  South  Carolina, 
Kansas,  and  New  York.  If  not  checked,  it  will  no 
doubt  spread  rapidly  and  add  to  the  burdens  of  losses 
from  other  troubles. 

Symptoms.  On  the  fruit  the  disease  is  charac- 
terized by  conspicuous  dark  spots  (fig.  65  e)  on  the 
side  and  at  the  stem  end  of  both  green  and  mature 
fruit.  On  the  surface  of  the  largest  spots  numerous 
dark  pycnidia  may  be  seen.  Besides  attacking  the 
fruit,  the  disease  may  also  attack  the  foliage,  causing 
dark  spots  which  resemble  those  on  the  fruit  (fig. 
65  d).  Affected  leaves  shrivel,  droop,  and  sometimes 
drop  off.  The  disease  seems  to  be  unable  to  attack 
potatoes  or  peppers. 

The  Organism.  The  mycelium  (fig.  65  h)  forms  a 
dense  network  of  fungal  threads  within  the  host 
tissue.  The  pycnidia  (fig.  65  g)  are  subglobose,  car- 
bonaceous, smooth,  slightly  papillate,  and  with  a  dis- 
tinct central  pore.  The  pycnidia  are  scattered  and 


-    <•;> 


*v   <Cw:'' 

Wv., 


FIG.  65.     TOMATO  DISEASES. 

a.  Various  forms  of  vegetative  cells  of  the  yeast  rot  fungus,  b.  ascus,  j.  ascosporeh 
of  the  yeast  rot  fungus  (a.  to  c.  after  Schneider),  d.  Phoma  rot  on  foliage,  e.  Phoma 
rot  on  fruit,/,  pycnidium  of  the  Phoma  rot  organism,  g.  cross-section  of  a  pycnidium 
of  the  Phoma  fungus,  h.  mycelium,  ».  pycnospores  of  same  (d.  to  i.  after  Jamieson). 


FIG.  66.     TOMATO  DISEASES. 

a.  Septoria  leaf  spot,  b.  section  through  a  pycnidium  of  Septoria  lycopersici 
(after  Levin),  c.  section  through  acervulus  of  Colletotrichum  phomoides  (after  Venus 
Pool),  d.  and  e.  Melanconium  rot,  /.  section  through  an  acervulus  of  the  Melan- 
conium  fungus  (d.  to/,  after  Tisdale). 


Family  Solanaceae  347 

possess  a  thin  wall;  the  pycnospores  (fig.  65  i)  are 
hyalin  and  one-celled.  Jamieson1  failed  to  find  an 
ascus  or  winter  stage.  Should  the  disease  become 
serious,  spraying  with  Bordeaux  is  recommended. 

LEAF  SPOT 
Caused  by  Septoria  lycopersici  Speg. 

The  disease  is  generally  known  as  late  blight,  or 
blight,  both  of  which  names  are  misleading.  Recent 
investigations  by  Levin2  confirm  the  belief  that  leaf 
spot  is  widely  distributed.  It  is  found  in  Alabama, 
California,  Connecticut,  Delaware,  Illinois,  Louisiana, 
Massachusetts,  Maryland,  Michigan,  Missouri,  New 
Jersey,  New  York,  North  Carolina,  Ohio,  Penn- 
sylvania, Virginia,  Tennessee,  Texas,  and  Wisconsin . 

Symptoms.  The  first  indications  of  the  disease 
are  minute  water-soaked  spots  on  the  underside  of  the 
leaves.  With  time  these  increase  in  size  and  become 
circular  in  outline  with  a  definite  margin  (fig.  66  a) . 
The  spots  become  hard,  dry,  dark,  and  shrunken,  and 
when  numerous  they  coalesce  into  large  blotches,  in- 
volving the  entire  leaflets  and  leaves ;  the  latter  soon 
droop,  dry,  and  cling  to  the  stalk,  until  broken  off  by 
the  wind  or  by  any  other  jar.  Within  the  spots  are 
formed  minute  black  glistening  pycnidia  and  the 
spores  exude  as  yellowish  mucilaginous  drops. 

On  the  stems  the  spots  are  similar  to  those  on  the 
leaves,  although  they  are  not  so  clearly  defined,  nor 

1  Jamieson,  C.  O.,  U.  S.  Dept.  Agr.  Research,  4  :  1-20,  1915. 

2  Levin,  E.,  Michigan  Agr.  Expt.  Sta.  Tech.  Bui.  25  :  7-51,  1916. 


348  Diseases  of  Truck  Crops 

do  they  work  in  deep  to  form  cankers.  Spots  may 
also  occur  on  the  calyx  and  on  the  fruit.  The  dis- 
ease, however,  is  usually  a  foliage  trouble.  Of  the 
more  resistant  varieties  maybe  mentioned  Mikado, 
King  Humbert,  Wonder  of  the  Market,  and  Up  to 
Date.  Of  the  medium  resistant  varieties  may  be 
mentioned  Alice  Roosevelt,  President  Garfield,  Pre- 
lude, Ponderosa,  and  Magnum  Bonum.  The  Trophy 
and  Ficarazzi  are  very  susceptible  varieties. 

The  Organism.  The  mycelium  of  Septoria  lyco- 
persici  is  hyalin,  septate.  The  pycnidia  are  globose 
(fig.  66  b)  ;  the  pycnospores  are  hyalin,  needle-shaped, 
many-septate,  and  lose  their  vitality  when  exposed  to 
ordinary  room  temperature  for  about  four  days. 

Control.  The  disease  often  starts  on  the  seedlings 
in  the  seed  bed.  It  is  important  therefore  to  start 
with  a  clean  seed  bed  soil.  Seedlings  should  be 
sprayed  with  4-4-50  Bordeaux  before  being  trans- 
planted. In  the  field  the  plant  should  not  be  worked 
in  wet  weather,  or  when  covered  with  dew.  Spraying 
with  4-4-50  Bordeaux  is  recommended,  especially  in 
wet  weather.  Since  the  causative  fungus  is  carried 
over  in  pycnidia  on  dead  leaves  or  stems,  the  burn- 
ing of  all  trash  becomes  necessary. 

ANTHRACNOSE 
Caused  by  Colletotrichum  phomoides  (Sacc.)  Chester. 

Anthracnose  is  a  disease  to  which  ripe  tomatoes 
are  especially  subject.  The  losses  are  often  consid- 
erable both  in  the  field  and  in  transit. 


Family  Solanaceae  349 

Symptoms.  The  spots  are  at  first  small,  but  they 
soon  enlarge.  They  are  discolored,  sunken,  wrinkled, 
with  distinct  central  zones,  closely  resembling  the 
anthracnose  of  apple.  In  moist  weather  the  spots 
become  coated  with  a  salmon-colored  layer  which 
consists  of  the  spores  of  the  fungus. 

The  Organism.  In  structure  C.  phomoides  is  little 
different  from  other  Colletotrichums.  The  setae  of 
the  fungus  are  very  numerous,  thus  giving  the  acer- 
vuli  a  black  appearance.  The  conidiophores  are 
short,  and  the  conidia,  oblong,  hyalin,  and  one-celled 
(fig.  66  c). 

Control.  Anthracnose  depends  upon  wet  weather 
for  its  activity.  Spraying  with  Bordeaux  is  recom- 
mended. 

MELANCONIUM  ROT 
Caused  by  Melanconium  Tisdale  Taub. 

Melanconium  rot  is  a  disease  which  attacks  tomato 
fruit.  Tisdale1  was  the  first  to  call  attention  to  this 
trouble  which  he  attributed  to  a  species  of  Melan- 
conium. The  writer  has  often  had  occasion  to  col- 
lect this  disease  on  tomatoes  in  the  Bryan  (Texas) 
market.  The  origin  of  the  fruits  could  not  be  exactly 
ascertained,  but  they  were  supposed  to  come  from 
Florida,  while  others  were  home-grown. 

Infection  experiments  by  the  author  affirm  the 
parasitic  nature  of  the  organism,  which  is  tempor- 
arily named  Melanconium  Tisdale  Taubenhaus. 

«  Tisdale,  W.  H.,  Phytopath.  6  : 390-394,  1916. 


35°  Diseases  of  Truck  Crops 

Symptoms.  The  disease  is  found  both  on  partly 
green  and  on  ripe  fruit.  The  spots  are  brown  to 
black,  small,  irregular,  somewhat  sunken,  dry,  and 
superficial,  with  the  centers  slightly  raised  (fig.  66 
d-e). 

The  Organism.  The  mycelium  is  white,  much 
branched,  and  closely  septate,  the  septation  however 
being  largely  influenced  by  food  supply.  The  co- 
nidiophores  are  straight,  short,  closely  packed  to- 
gether, arising  from  a  basal  pseudostroma  (fig.  66  f) . 
The  conidia  are  borne  singly  at  the  apex  of  each  co- 
nidiophore.  The  conidia  are  Phoma-like,  minute, 
cylindrical,  slightly  rounded  at  both  ends,  greenish 
white  in  color,  and  germinate  by  means  of  a  single 
germ  tube  produced  at  either  end. 

Control.  Nothing  seems  to  be  known  of  the  control 
of  this  trouble.  Little  is  known  of  its  distribution. 
But  since  it  has  been  found  in  Wisconsin  by  Tisdale, 
and  in  Texas  by  the  writer,  it  seems  to  be  of  wider 
distribution  than  is  generally  recognized.  Possibly 
it  is  usually  mistaken  for  other  tomato  troubles. 

LEAF  MOLD 
Caused  by  Cladosporium  fulvum  Cke. 

Leaf  mold  is  a  tomato  trouble  which  is  very 
troublesome  under  greenhouse  conditions.  In  some 
of  the  Southern  States,  however,  it  is  found  on  field 
tomatoes.  The  disease  is  favored  by  damp,  muggy 
weather. 

Symptoms.     The  mold  appears  as  rusty  cinnamon, 


FIG.  67.     TOMATO  DISEASES. 

a.  Cladosporium  leaf  mold,  b.  conidiophores  of  Cladosporiunt  fulvum,  c.  conidia  of 
C.  fulvum,  (b.  and  c.  after  Southworth)',  d.  two  plants  artificially  infected  with 
Sclerotium  Rolfsii,  e.  sunburn,  /.  Macrosporium  rot. 


Family  Solanaceae  351 

irregular,  feltlike  spots  on  the  underside  of  the  leaf 
(fig.  67  a),  the  upper  part  of  which  turns  brown,  then 
black,  and  the  affected  foliage  finally  curls  and  dies. 
Control.  Careful  spraying  with  Bordeaux  mixture 
will  help  to  keep  it  in  check. 

BLACK  ROT 

Caused  by  Macrosporium  solani  E.  and  M. 

Black  rot  is  a  fruit  trouble  commonly  found  in  dry 
weather  and  generally  attacking  ripe  tomatoes. 
The  spots  are  black,  dry,  slightly  wrinkled,  and  ex- 
tending deep  into  the  interior  tissue  (fig.  67  f). 

The  mycelium  of  the  fungus  is  at  first  hyalin  to 
brown,  then  black.  The  conidiophores  and  conidia 
are  dark,  with  three  to  six  transverse  and  one  to  two 
longitudinal  septa. 

SLEEPING  SICKNESS 
Caused  by  Fusarium  lycopersici  Sacc. 

Sleeping  sickness  is  one  of  the  most  serious  of 
tomato  troubles.  It  is  prevalent  in  New  Jersey, 
Delaware,  Maryland,  Virginia,  and  in  nearly  every 
Southern  State. 

Symptoms.  Infected  plants  become  pale,  the 
leaves  wilt  and  droop  and  never  recover  (fig.  68). 
The  droopiness  of  a  diseased  plant  gives  it  a  sleepy 
appearance,  hence  the  name  of  the  disease.  On 
splitting  open  a  diseased  root  or  stem,  the  interior 
vascular  bundles  will  be  found  to  be  brown. 


352  Diseases  of  Truck  Crops 

The  Organism.  F.  ly coper sici  is  a  soil  fungus 
which  may  be  introduced  with  infected  manure  or 
seedlings.  The  fungus  greatly  resembles  F.  oxy- 
sporum.  The  conidia  are  hyalin  to  yellowish,  fal- 
cate, acute. 

Control.  Spraying  will  not  control  this  malady 
since  the  parasite  lives  internally  and  cannot  be 
reached  by  external  applications.  Long  rotations 
in  which  the  land  is  given  a  rest  from  tomatoes  are 
recommended  for  at  least  ten  years.  The  selection 
of  resistant  varieties  may  offer  a  means  of  conquering 
this  trouble. 

YELLOW  BLIGHT 

Caused  by  Fusarium  orihoceras  App.  and  WolL; 
Fusarium  oxysporum  Schl. 

This  disease  is  common  on  tomatoes  in  the  Pacific 
Northwest.  It  has  been  investigated  by  Humphrey1 
and  found  by  him  to  be  caused  by  the  two  species  of 
Fusaria  above  mentioned. 

Symptoms.  It  does  not  usually  manifest  itself 
until  late,  when  the  plants  are  blooming,  or  even 
when  the  fruits  are  partly  formed.  At  first  there  is 
a  slight  twisting  of  the  entire  leaf,  accompanied  by  a 
purpling  of  the  veins.  This  is  also  followed  by  a 
rolling  inward,  and  by  drooping,  but  not  wilting,  of 
the  leaflets  and  leaves.  The  foliage  then  take  on 
glaucous  greenish  color,  the  fruit  ripen  prematurely, 

1  Humphrey,  H.  B.,  Washington  Agr.  Expt.  Sta.  Bui.  115  : 1-22, 
1914. 


FIG.  68.     vSLEEPiNG  SICKNESS  OF  TOMATO. 


Family  Solanaceae  353 

but  the  pulp  lacks  in  flavor  and  taste.  Affected 
plants  cease  growing,  exhibit  a  thin,  spindly  growth, 
and  cease  producing.  The  disease  is  confined  to  the 
root  system,  which  is  slowly  destroyed;  it  becomes 
most  virulent  with  the  high  temperatures.  Both 
Fusarium  orthoceras  and  F.  oxysporum  also  induce 
a  disease  on  the  potato,  see  p.  327. 

Control.  Both  Fusaria  produce  an  abundance  of 
chlamydospores  in  the  soil,  thus  making  the  eradica- 
tion of  the  disease  very  difficult.  Long  rotations 
seem  to  have  no  effect  in  controlling  the  trouble. 
Injuring  the  rootlets  at  transplanting  seems  to  in- 
crease the  amount  of  diseased  plants.  Definite 
methods  of  control  are  as  yet  lacking. 

RHIZOCTONIA  FRUIT  ROT 

Caused  by  Corticium  vagum  B.  and  C.  var.  solani 
Burt. 

This  form  of  rot  makes  its  appearance  at  the  place 
where  the  fruit  touches  the  ground.  The  diseased 
area  becomes  chocolate-colored,  and  the  epidermis 
slightly  wrinkled.  The  rot  extends  into  the  interior 
pulp  turning  it  brown  and  dry.  For  further  descrip- 
tion of  the  causative  fungus,  see  p.  45. 

SOUTHERN  BLIGHT  (fig.  67  d),  see  PEPPER,  p.  305. 

ROOT  KNOT,  see  NEMATODE,  p.  49. 

23 


CHAPTER  XXII 

FAMILY  UMBELLIFER.E 

THIS  family  contains  trucking  crops  which  are  of 
considerable  economic  importance.  Of  these  may 
be  mentioned  the  carrot,  celery,  parsley,  and  parsnip. 
According  to  the  Thirteenth  census  of  the  United 
States,  the  area  devoted  to  carrots  in  the  United 
States  in  1909  was  3764  acres,  and  the  total  crop  was 
valued  at  $473,499,  with  New  York  leading  in  acreage. 
The  area  devoted  to  celery  in  1909  was  15,863  acres, 
and  the  total  crop  estimated  at  $3,922,848.  Of  the 
leading  celery  States  may  be  mentioned  New  York, 
California,  Michigan,  Ohio,  Massachusetts,  and 
Pennsylvania.  The  area  in  parsley  in  1909  was  192 
acres,  and  the  crop  estimated  at  $2  7 , 1 8 1 .  Thi  s  crop  is 
largely  grown  in  Louisiana.  The  area  in  parsnip  in 
1909  was  722  acres,  and  the  crop  estimated  at  $102,- 
674.  Parsnip  is  grown  mainly  in  New  York,  Massa- 
chusetts, Illinois,  and  Michigan. 

DISEASES  OF  THE  CARROT  (Daucus  carota) 

SOFT  ROT,  see  CABBAGE,  p.  192. 
ROOT  ROT,  see  RHIZOCTONIA,  p.  45. 

354 


Family  Umbelliferae  355 

DISEASES  OF  THE  CELERY  (Apium  graveolens) 
SOFT  ROT,  see  CABBAGE,  p.  192. 

RUST 
Caused  by  Puccinia  bullata  (Pers.)  Schr. 

This  rust  resembles  the  rust  of  asparagus.  The 
disease  is  unimportant,  and  is  seldom  met  with  in 
the  United  States. 

LEAF  SPOT 
Caused  by  Phyllosticta  apii  Hals. 

Leaf  spot  is  a  disease  of  minor  importance.  The 
trouble  is  characterized  by  dull  brown  patches  on  any 
part  of  the  leaf.  Spraying  for  late  blight  will  also 
control  leaf  spot. 

LATE  BLIGHT 

Caused  by  Septoria  petroselini  Desm.  var.   apii 
Br.  and  Cav. 

Late  blight  is  perhaps  one  of  the  worst  diseases  of 
celery.  It  may  be  found  wherever  celery  is  grown. 
In  California,  the  greatest  money  losses  to  this  crop 
are  attributed  to  late  blight. 

Symptoms.     The  disease  first  attacks  the  lower 


356  Diseases  of  Truck  Crops 

leaves  of  the  stalk,  producing  irregular  spots  without 
a  definite  boundary  line.  When  the  spots  become 
numerous  the  foliage  withers  and  dries  up  (fig.  69  a, 
b,  c,  d).  The  disease  attacks  the  leaves  as  well  as 
the  stalks,  rendering  the  affected  plants  useless  so  far 
as  market  is  concerned.  In  storage,  plants  affected 
with  late  blight  will  keep  very  poorly  or  rot  alto- 
gether. 

The  Organism.  The  fungus  mycelium  is  hyalin, 
septate.  The  pycnidia  (fig.  69  e)  are  olivaceous, 
prominent,  and  abundant  in  the  spots.  The  pycnidia 
are  filifom,  straight  or  curved,  hyalin,  and  many 
septate. 

Control.  According  to  Rogers,1  late  blight  may 
be  controlled  by  spraying  with  5-6-50  Bordeaux. 

The  first  two  applications  should  be  given  the 
seedlings  in  the  seed  bed.  In  the  field  the  first 
spraying  should  be  given  about  six  weeks  after  trans- 
planting and  continued  once  a  month  until  the  rainy 
season  is  over.  With  the  advent  of  heavy  rains, 
spraying  should  be  done  once  every  two  weeks. 
Besides  spraying,  shading  also  seems  to  keep  the 
disease  in  check.  In  spraying  celery  great  care 
should  be  exercised  to  use  a  sprayer  which  is  operated 
by  a  pressure  of  not  less  than  1 50  pounds.  Where  this 
is  overlooked,  large  drops  of  the  Bordeaux  mixture 
maybe  deposited  on  the  leaves  and  stalks,  which  upon 
drying  may  deposit  copper  salt  sufficient  to  harm 
the  consumer.  Sprayed  celery  should  be  carefully 
washed  and  dried  before  shipping. 

1  Rogers,  S.  S.,  California  Agr.  Expt.  Stat.  Bui.  208  :  83-115, 1911. 


i 


FIG.  69.  CELERY  DISEASES. 

a.   Septoria  leaf  spot  on  leaf,  b.  Septoria  leaf  spot  on  leaflet,  c.  Septoria  lesions  on 
relery  seed,  d.  Septoria  spots  showing  pycnidial  bodies,  e.  cross  section  showing 

Eyncidium    and    pycnospores  of  Seploria  petroselini  (a,  c,  and   e  after  Coons  and 
evin). 


FIG.  70.     CELERY  DISEASES. 

a.  Cercospora  leaf  spot,  6.  conidiophores  and  conidia  of  Cercospora    apii 
(afterDuggar  and  Baily),  c.  Rhizoctonia  root  rot. 


Family  Umbelliferae  357 

EARLY  BLIGHT 
Caused  by  Cercospora  apii  Fr. 

Early  blight  is  as  common  a  disease  as  the  late 
blight.  In  some  seasons  of  heavy  rains  it  is  very 
destructive.  It  appears  early  and  affected  plants 
have  little  value  for  market  purposes. 

Symptoms.  The  trouble  first  appears  on  the  outer 
leaves  as  pale  blotches  visible  on  both  sides  of  the 
affected  parts.  The  spots  are  irregular,  angular  in 
outline,  limited  apparently  by  the  leaf  veins,  with 
slightly  raised  borders  (fig.  70  a-b).  The  spots  later 
turn  brown  to  ashy  white. 

Control.  Early  blight  may  be  controlled  by  spray- 
ing with  Bordeaux  mixture  as  with  late  blight.  The 
Boston  Market  and  Gold  Heart  should  be  avoided 
because  of  their  susceptibility  to  the  disease.  The 
White  Plume  seems  to  be  resistant. 

DISEASES  OF  PARSLEY  (Carum  petroseHnum) 

DROP,  see  LETTUCE,  p.  143. 

LATE  BLIGHT,  see  CELERY,  p.  355. 

DISEASES  OF  THE  PARSNIP  (Pastinaca  sativd) 

EARLY  BLIGHT,  see  CELERY,  p.  357. 

ROOT  ROT  (fig.  70  c),  see  RHIZOCTONIA,  p.  45. 

WEEDS 

Of  the  more  important  Umbelliferous  weeds  which 
truckers  have  to  contend  with  may  be  mentioned 


35$  Diseases  of  Truck  Crops 

Wild  Carrot  (Daucus  carsta) ,  wild  parsnip  (Pastinaca 
sativa),  and  poison  hemlock  (Cornium  maculatum) . 
All  of  these  weeds  should  be  eradicated  by  clean  cul- 
ture. The  first  two  especially  help  to  carry  the 
fungus  of  early  blight,  Cercospora  apii. 


PART  IV 


359 


CHAPTER  XXIII 

METHODS  OF  CONTROL 

FROM  the  preceding  chapters  the  trucker  will  be 
made  well  aware  of  the  many  crop  diseases  he  has  to 
deal  with  and  of  the  numerous  methods  at  hand  to 
help  him  to  control  or  keep  in  check  most  of  the 
troubles.  The  methods  of  control  may  be  classified 
as  follows: 

(1)  Soil  sterilization.    This  method  has  been  dis- 
cussed under  Chapter  IV,  page  53. 

(2)  Seed  treatment  taken  up  in  Chapter  VII. 

(3)  Spraying. 

(4)  Crop  rotation. 

(5)  Development  of  resistant  varieties. 

Spraying 

While  the  orchardist  has  learned  the  necessity  of 
spraying,  it  is  doubtful  whether  truckers  have  suf- 
ficiently realized  its  value.  Spraying  has  two  aims : 
to  kill  the  insect  and  animal  pests,  and  to  con- 
trol fungous  diseases.  The  substances  which  are 
used  for  the  one  purpose  are  without  effect  on  the 
other. 

361 


362  Diseases  of  Truck  Crops 

INSECTICIDES 

All  animal  and  insect  pests  are  best  controlled  by 
the  use  of  poisonous  mixtures  applied  in  the  form  of 
liquid  sprays  or  of  powders.  Insecticides  may  be 
classified  as  internal  or  stomach  poisons,  and  external 
or  contact  poisons. 

(a)  Stomach  Poisons.  Paris  green  is  one  of  the 
oldest  of  stomach  poisons.  When  chemically  pure, 
it  is  composed  of  copper  oxide,  acetic  acid,  and  arseni- 
ous  acid.  It  destroys  cutworms,  caterpillars,  beetles, 
grubs,  slugs,  etc.  It  should  be  applied  preferably  as 
a  liquid,  using  one  pound  of  the  poison  and  two 
pounds  of  lime  to  two  hundred  gallons  of  water.  It 
tends  to  sink  to  the  bottom  of  this  mixture,  unless 
constantly  stirred  while  being  applied.  This  chemi- 
cal is  often  adulterated  with  white  arsenic,  causing 
it  to  scorch  the  treated  plants  badly.  Therefore 
for  truck  crops  the  use  of  arsenate  of  lead  is  to  be 
preferred,  since  it  is  less  liable  to  scorch  the  foliage, 
and  it  adheres  better.  Its  chemical  composition 
consists  of  acetate  of  lead  and  arsenate  of  soda.  It 
is  applied  to  the  best  advantage  as  a  liquid,  using 
about  three  pounds  of  powdered  arsenate  or  five 
pounds  of  paste  arsenate  to  one  hundred  gallons  of 
water. 

Arsenite  of  zinc  may  also  be  used.  It  is  a  very 
finely  divided  fluffy  white  powder  which  distributes 
and  adheres  well  to  the  foliage.  It  is  intermediate 
between  Paris  green  and  lead  arsenate  in  strength, 
and  it  costs  less  than  either. 


Methods  of  Control  363 

//  is  essential  when  arsenicals  are  used  to  see  that 
they  are  correctly  labeled,  and  kept  under  lock  and  key, 
as  they  are  poisonous  to  man  and  animals. 

Hellebore  or  white  hellebore  is  somewhat  less 
dangerous  than  the  arsenicals.  However,  it  loses 
its  insecticidal  value  by  being  exposed  to  the  air. 
It  is  a  specific  against  slugs. 

(b)  Contact  Poisons.  All  the  tobacco  or  nicotine 
products  sold  principally  as  extracts  or  powders  be- 
long to  this  class.  A  common  brand  much  used  is 
the  preparation  known  as  "Black  leaf  40,"  diluted 
I  part  to  700  or  800  of  water.  An  addition  of 
ivory  soap  at  the  rate  of  two  bars  to  each  100 
gallons  of  the  solution  increases  its  effectiveness 
by  making  it  spread  out  better.  Aphine,  sulpho 
tobacco,  and  a  number  of  other  products  found  on 
the  market  are  usually  valuable  as  contact  poisons 
if  properly  tested  out  and  guaranteed  by  the  deal- 
ers. Ordinary  laundry  soap,  one  pound  to  seven 
gallons  of  water,  is  very  effective  against  all  soft- 
bodied  sucking  insects. 

FUNGICIDES 

These  are  poisons  used  to  control  fungous  diseases. 
As  previously  stated,  some  parasitic  fungi  live  on  the 
surface  of  the  leaves  and  stems  and  are  therefore 
easily  controlled.  An  example  of  this  is  the  powdery 
mildew.  Other  fungi,  and  these  are  in  the  larger 
majority,  are  those  which  live  parasitically  within 
the  tissue  of  the  host,  and  therefore  cannot  be  reached 


364  Diseases  of  Truck  Crops 

by  any  spray.  Fungicides  are  helpful  only  in  pre- 
venting entrance  of  the  parasite  in  the  host.  They 
are  as  ineffective  in  controlling  insect  pests,  as  are 
insecticides  in  controlling  fungous  diseases. 

(a)  Bordeaux  Mixtures.  This  is  the  standard 
fungicide.  The  strength  used  for  tender  plants  is 
three  pounds  of  copper  sulphate — also  known  as  blue 
stone, — six  pounds  of  lime,  and  fifty  gallons  of  water. 
The  easiest  way  to  prepare  it  is  to  dissolve  the  blue 
stone  thoroughly  in  twenty-five  gallons  of  water. 
The  best  quality  of  unslaked  lime  should  be  used 
and  slaked  in  a  little  hot  water,  care  being  taken, 
however,  not  to  flood  it  while  slaking,  nor  to  let  it 
become  too  dry.  When  the  slaking  is  completed, 
enough  water  is  added  to  make  twenty-five  gallons. 
The  limewater  and  the  blue  stone  solution  are 
then  mixed,  pouring  first  one  part  of  lime  water,  then 
another  part  of  the  blue  stone;  the  mixture  is  then 
strained  and  used  at  once.  With  crops  with  delicate 
foliage,  such  as  watermelon,  weak  Bordeaux  must  be 
used  to  prevent  burning  of  foliage  (see  page  243). 

For  truck  crops  with  less  delicate  foliage,  the  stand- 
ard Bordeaux  mixture  is  4-4-50 — that  is,  four  pounds 
copper  sulphate,  four  pounds  unslaked  lime,  and 
fifty  gallons  of  water. 

Stock  Solutions.  In  spraying  large  areas,  it  is  not 
always  practical  to  weigh  out  and  prepare  the  in- 
gredients at  short  notice.  The  trucker  will  therefore 
find  it  advantageous  to  prepare  stock  solutions  so 
that  large  quantities  of  both  dissolved  copper  sul- 


Methods  of  Control  365 

phate  and  of  lime  may  be  ready  for  instant  use.     A 
stock  solution  of  blue  stone  may  be  prepared  as 
follows:    Forty  gallons   of  water   are   put  into  a 
fifty-gallon  barrel;  forty  pounds  of  blue  stone  are 
placed  in  a  basket  and  hung  up  so  that  the  basket  is 
half  covered  by  the  water  in  the  barrel.    As  the  blue 
stone  is  dissolved,  each  gallon  of  the  water  contains 
one  pound  of  the  chemical.     In  another  barrel  may 
be  slaked  forty  pounds  of  fresh  lime.     Each  gallon  of 
that  will  contain  one  pound  of  lime.     By  keeping  the 
slaked  lime  in  the  barrel  covered  with  water  and  pre- 
venting it  from  evaporating,  and  also  keeping  the 
barrel  with  the  blue  stone  solution  covered  to  prevent 
evaporation,  we  shall  have  stock  solutions  ready  for 
instant  use.     To  make  a  4-4-50  Bordeaux  from  stock 
solutions,  for  instance,  it. is  necessary  to  take  four 
gallons  from  the  stock  solution   barrel  with  blue 
stone,  and  add  this  to  twenty-one  gallons  of  water. 
Four  gallons  are  also  taken  from  the  stock  solution 
barrel  of  slaked  lime  and  added  to  twenty-one  gal- 
lons of  water.    The  two  solutions  of  twenty-five 
gallons  each  are  now  added  together,  thus  making  a 
4-4-50  Bordeaux.     In  this  way  it  is  easy  to  prepare 
any  formula  from  the  stock  solutions.     To  determine 
if  the  Bordeaux  contains  sufficient  lime,  the  following 
test  may  be  carried  out.    A  few  drops  of  potassium 
ferrocyanide  are  added  to  the  Bordeaux  mixture. 
If  sufficient  lime  is  present,  no  change  will  take  place, 
but  if  the  mixture  is  deficient  in  lime,  a  dark  reddish 
brown  color  will  appear  where  the  drop  strikes  the 
liquid.     This  testing  fluid  is  easily  prepared  by  dis- 


366  Diseases  of  Truck  Crops 

solving  one  ounce  of  potassium  ferrocyanide  in  about 
eight  ounces  of  water.  This  chemical  costs  but  a  few 
cents  in  any  drug  store  and  will  last  a  long  time  if 
kept  in  a  tightly  sealed  bottle. 

POINTS  TO  BE  REMEMBERED 

In  preparing  Bordeaux  the  following  points  should 
be  kept  in  mind : 

(1)  Copper  sulphate  solutions  must  be  kept  only  in 
vessels  of  wood,  fiber,  brass,  bronze,  or  copper.     They 
must  not  be  kept  in  iron  or  tin  vessels,  as  they  will 
corrode  them. 

(2)  It  is  necessary  to  use  fresh  stone  lime,  as  air- 
slaked  lime  is  useless. 

(3)  Bordeaux  mixture  can   be  used  only  when 
freshly  mixed.     If  allowed  to  stand  twelve  hours  after 
making,  it  loses  all  fungicidal  value. 

(4)  Bordeaux  mixture  or  lime  should  never  be 
strained  through  burlap.     The  lint  of  the  burlap  is 
likely  to  work  up  into  the  nozzles  and  clog  them. 

(5)  Undiluted  solutions  of  copper  sulphate  or  lime 
should  never  be  mixed  together. 

(6)  Bordeaux  mixture  should  not  be  prepared  with 
hot  water. 

(b)  Ammoniacal  Copper  Carbonate.  The  objection 
to  the  use  of  Bordeaux  is  that  it  stains  the  leaves 
and  foliage. 

To  avoid  staining,  colorless  ammoniacal  copper 
carbonate  may  take  the  place  of  Bordeaux.  It  is 
prepared  as  follows: 


Methods  of  Control  367 

Copper  carbonate 5  ounces 

Ammonia  (26  Baume) 3  pints 

Water . 50  gallons 

The  best  results  are  obtained  when  the  copper  car- 
bonate is  first  made  into  a  paste  with  a  little  water. 
It  is  then  dissolved  by  adding  the  ammonia,  which  is 
diluted  with  four  quarts  of  water.  If  three  pints 
of  ammonia  fail  to  dissolve  all  the  copper  carbonate, 
more  may  be  used.  Ammoniacal  copper  carbonate 
is  only  effective  when  used  fresh.  It  loses  its  fungi- 
cidal  value  by  standing,  as  the  ammonia  evaporates 
quickly. 

(c)  Sulphur.  Flowers  of  sulphur  are  often  used  to 
control  powdery  mildew  or  asparagus  rust.  It  may 
be  applied  either  by  hand  or  with  a  duster.  There 
are  a  number  of  other  fungicides  on  the  market  which 
are  not  mentioned  here.  They  should  be  thoroughly 
tested  before  they  are  used.  Considerable  discretion 
should  be  exercised  before  using  a  new  fungicide 
which  claims  to  be  a  ' '  Cure  all. " 

COMBINATION  SPRAYS 

In  the  foregoing  chapters  on  diseases,  it  was  seen 
that  truck  crops  are  subject  to  the  attacks  of  more 
than  one  malady.  Moreover,  truck  crops  are  also 
subject  to  the  attacks  of  insect  pests.  It  is  therefore 
advisable  to  control  both  insect  pests  and  fungous 
diseases  at  the  same  time.  Spraying,  if  properly 


368     Diseases  of  Truck  Crops 

done,  is  effective  in  controlling  or  in  keeping  in  check 
all  the  pests  which  attack  truck  crops.  In  combining 
a  fungicide  with  an  insecticide,  we  may  accomplish 
two  aims  in  one  operation.  The  various  spray  mix- 
tures which  may  or  may  not  be  combined  are  in- 
dicated by  Cooley  and  Swingle1  as  follows: 

Tobacco     Bordeaux 
extracts        mixture 

Paris  green  yes  yes 

Arsenate  of  lead  yes  yes 

Arsenite  of  zinc  (ortho)  yes  no 

Arsenite  of  lime  yes  yes 

Each  of  these  preparations  is  mixed  and  applied  just 
as  if  it  were  used  alone.  A  combination  of  the  am- 
moniacal  copper  carbonate  with  an  arsenate  would  be 
unsafe,  since  the  ammonia  renders  the  arsenic  more 
soluble,  and  hence  may  result  in  the  burning  of  the 
foliage.  However,  it  may  be  safely  mixed  with  the 
tobacco  products. 

Recent  investigations  by  Professor  Safro,  Entomo- 
logist to  the  Kentucky  Tobacco  Products  Co.,  indi- 
cate that  * '  Black  leaf  40 ' '  may  be  used  in  combination 
with  such  spray  chemicals  as  lime-sulphur,  arsenate 
of  lead,  arsenite  of  zinc,  and  iron  sulphate,  for  con- 
trolling sucking  and  chewing  insects  and  fungous  dis- 
eases, the  soap  in  this  case  being  omitted.  Professor 
Safro 's  work  further  claims  that  "  Black  leaf  40  "  may 

1  Cooley,  B.  A  ,  and  Swingle,  D.  B.,  Montana  Agr.  Expt.  Sta.  Circ. 
17: 


Methods  of  Control  369 

be  safely  combined  with  Bordeaux,  and  the  desired 
results  obtained.  He  writes  as  follows:  "For  pur- 
poses of  spraying,  add  to  every  one  hundred  gallons  of 
Bordeaux  three  fourths  of  a  pint  of  '  Black  leaf  40. ' 
As  far  as  safety  to  the  foliage  is  concerned,  much 
greater  strengths  of  nicotine  may  be  added  to  the 
Bordeaux,  but  no  additional  effectiveness  will  be 
given  to  the  mixture  as  an  insecticide.  Any  nicotine 
solution  which  contains  four  hundredths  of  one  per 
cent,  nicotine  will  be  effective  in  controlling  plant  lice, 
provided,  however,  the  work  is  thoroughly  done." 

PROPORTIONS  OF  COMBINED  SPRAYS 
Bordeaux  and  Paris  Green 

Paris  Green y£  pound 

Bordeaux  mixture 50  gallons 

Bordeaux  and  Ar senile  of  Soda 

Arsenite  of  Soda I    quart 

Bordeaux  mixture 50  gallons 

Bordeaux  mixture  must  never  be  combined  with 
kerosene  emulsion,  carbolic  acid  emulsion,  and  mis- 
cible  oils. 

(d)  Potassium  Sulphide.  Like  sulphur  this  is  a 
valuable  fungicide  for  the  control  of  the  powdery 
mildew.  The  following  strength  is  recommended: 

Potassium  Sulphide 4  oz. 

Water 10  gallons 

24 


370     Diseases  of  Truck  Crops 

Potassium  sulphide  is  effective  only  if  used  imme- 
diately it  is  prepared.  It  loses  its  value  by  being 
exposed  for  any  length  of  time. 

STICKERS 

It  is  well  known  that  with  some  plants,  such  as 
cabbage,  spray  mixtures  cannot  be  made  to  stick. 
The  use  of  a  sticker  added  to  the  spray  mixture  will 
largely  overcome  this  difficulty.  A  sticker  may  be 
prepared  as  follows: 

Resin 2  pounds 

Sal  Soda  (crystals). . .  I  pound 
Water i  gallon 

The  resin  and  the  sal  soda  should  be  added  to  one 
gallon  of  water  and  boiled  in  an  iron  kettle  for  one 
and  a  half  hours  until  clear.  For  plants  which  are 
hard  to  wet,  such  as  cabbage,  or  onions,  the  amount 
of  the  sticker  given  above  should  be  used  for  each 
fifty  gallons  of  Bordeaux  or  ammoniacal  copper  car- 
bonate. For  other  plants,  this  amount  is  added  to 
each  one  hundred  gallons  of  the  spray  mixture. 

PRINCIPLES  INVOLVED  IN  SPRAYING 

It  should  be  remembered  that  to  destroy  chewing 
insects,  such  as  caterpillars,  etc.,  the  stomach  poison 
must  be  evenly  distributed  all  over  the  plant.  This 
thorough  spraying  should  be  done  as  soon  as  the 
presence  of  the  pest  is  suspected.  Intelligent  and 
observant  growers  will  remember  the  time  of  ap- 


Methods  of  Control  37  * 

pearance  of  the  pest  every  year,  although  this  date 
depends  somewhat  on  the  climate  of  each  season. 
In  destroying  the  green  aphids,  the  contact  poison 
should  be  distributed  as  evenly  as  possible  on  the 
insect  itself.  It  is,  therefore,  best  to  spray  for  aphids 
when  they  are  actually  found  working  on  the  plants. 
To  check  chewing  insects  and  fungous  pests,  however, 
the  applications  are  made  before  the  parasites  appear. 
Before  spraying  it  is  necessary  to  have  well  in  mind 
which  organism  is  to  be  destroyed,  and  the  proper 
ingredients  to  be  used.  To  keep  fungous  pests  in 
check  it  is  necessary  to  have  the  plant  covered  with 
the  fungicide  all  the  time  infection  is  feared  or  sus- 
pected. This  spraying  is  preventive,  protecting  the 
plant  from  becoming  infected.  When  the  parasite 
has  penetrated  the  host,  spraying  is  of  little  value  in 
saving  the  infected  plant,  although  it  will  protect 
others  which  are  as  yet  healthy.  It  is  essential  that 
the  trucker  be  always  ready  to  spray.  Sometimes 
retardation  for  even  a  day  may  prevent  the  attain- 
ment of  positive  results.  The  timely  destruction  of 
one  insect,  or  of  one  spore,  means  the  destruction  of 
countless  generations  of  these  pests. 

Thoroughness  is  as  important  in  spraying  as  it  is  in 
everything  else  in  life.  Especially  is  this  true  for  the 
control  of  fungous  diseases. 

SPRAYING  MACHINES 

Success  in  spraying  often  depends  on  the  sprayer, 
and  especially  on  the  nozzle.  In  small  scale  garden- 


372  Diseases  of  Truck  Crops 

ing,  an  ordinary  knapsack  or  barrel  sprayer  (fig.  71  a) 
will  answer  the  purpose.  For  trucking  on  large 
areas  the  use  of  power  sprayers  (fig.  71  b)  becomes 
necessary.  It  is  difficult  to  recommend  the  use  of 
any  one  type  when  there  are  so  many  models  on  the 
market.  After  consulting  various  catalogues  and 
examining  types  of  spray  machines  at  the  county 
fairs  and  other  exhibits,  the  grower  will  be  in  a  posi- 
tion to  determine  the  kind  of  apparatus  best  adapted 
for  his  conditions.  A  good  power  sprayer  should  be 
capable  of  maintaining  a  pressure  of  at  least  one 
hundred  pounds  while  the  nozzles  are  open.  The 
sprayer  should  also  have  a  convenient  attachment  for 
spraying  four  rows  or  more,  and  should  also  possess 
a  device  by  which  each  row  can  be  sprayed  with 
either  single  or  double  nozzles.  Moreover,  all  the 
working  parts  must  be  easily  accessible,  simple,  and 
solidly  built. 

CARE  OF  THE  SPRAYING  MACHINE 

After  each  spraying  the  outfit  should  be  emptied 
and  carefully  cleansed  with  water.  Failure  to  do 
this  will  result  in  the  corroding  of  the  tank,  rods,  and 
nozzles. 

CROP  ROTATION 

Many  of  the  soil  diseases,  such  as  root  knot,  Fusar- 
ium  wilts,  etc.,  may  be  economically  controlled  by 
crop  rotation.  If  a  certain  disease  gains  a  foothold 
in  the  soil,  it  is  likely  to  become  progressively  serious, 


FIG.  71.     SPRAY  MACHINERY. 

a.   A  hand  power  pump,  b.  a  power  machine,  rear    view,    showing 
arrangement  for  spraying  three  rows  of  cucumbers  (after  W.  A.   Orton) 


Methods  of  Control  373 

as  the  particular  crop  which  the  disease  attacks  is 
grown  for  a  number  of  years  on  the  same  field,  the 
soil  becoming  thoroughly  permeated  by  the  mycelium 
and  spores  of  the  parasitic  organism.  If  the  infected 
land  is  planted  with  crops  not  subject  to  the  disease, 
the  parasitic  organism  will  sooner  or  later  die  for 
want  of  a  suitable  host  to  live  upon.  For  this  reason 
crop  rotation  plays  an  important  part  in  the  control 
of  numerous  truck  crops.  To  meet  with  success 
in  rotation,  the  trucker  must  know  what  crops  are 
subject  to  the  disease  to  be  controlled,  so  as  to  avoid 
them  temporarily  in  the  sick  land.  Weeds,  too,  are 
often  subject  to  the  same  diseases  as  the  cultivated 
crops.  Crop  rotation  often  fails  if  we  overlook  the 
importance  of  clean  culture. 

VARIETIES  RESISTANT  TO  DISEASE 

It  is  a  well-known  fact  that  not  all  varieties  of 
plants  are  alike  subject  to  the  same  disease.  In 
going  over  a  diseased  field,  we  find  that  while  a  large 
percentage  of  the  plants  may  be  dying,  some  few 
individuals  will  stand  up  and  thrive  in  spite  of  the 
disease.  If  these  individual  plants  are  perpetuated 
in  the  same  sick  field,  we  may  succeed  in  developing 
a  strain  or  variety  of  plant  which  will  produce  one 
hundred  per  cent,  healthy  individuals  in  the  same  sick 
soil.  On  this  principle  are  based  the  selection  and 
development  of  resistant  varieties.  Much  has  al- 
ready been  accomplished  in  this  direction  and  still 
more  is  to  be  expected  in  the  future. 


374  Diseases  of  Truck  Crops 

How  to  Develop  a  Resistant  Variety 

This  may  be  accomplished  by  selecting,  from  the 
sickest  piece  of  land  on  which  the  crop  is  growing,  the 
healthiest  individuals,  and  taking  the  seed  from  them. 
The  following  year  the  selected  seeds  are  again 
planted  on  the  same  infected  land.  The  best  in- 
dividual plants  from  this  sowing  are  selected  and  their 
seeds  saved.  By  continuing  this  method  of  selection 
for  a  number  of  years  it  may  be  possible  to  develop 
a  strain  which  will  yield  one  hundred  per  cent,  of 
healthy  plants  in  a  sick  soil.  To  maintain  the  purity 
of  the  selected  strain  as  well  as  its  resistance,  it  is 
necessary  to  reserve  a  plot  of  the  sick  soil,  upon  which 
the  selected  strain  is  grown  for  seed  purposes.  Care 
must  be  taken  toward  carrying  any  of  the  sick  soil 
of  this  plot  to  other  parts  of  the  field. 

Drawbacks.  With  some  crops  and  with  certain 
diseases  it  seems  hopeless  to  try  to  develop  a  resist- 
ant strain.  If  a  variety  is  resistant  to  one  disease 
it  may  be  susceptible  to  several  others,  which  are 
perhaps  more  serious.  The  resistance  may  often  be 
local,  in  which  case  it  becomes  necessary  to  develop 
resistant  types  for  each  local  condition.  Resistant 
varieties  often  may  not  embody  the  requirements  of 
the  market.  Nevertheless,  the  development  of  re- 
sistant strains  should  be  tried  wherever  it  gives 
any  promise  of  success. 


CHAPTER  XXIV 

CONTROL  OF  INSECT  PESTS  BY  NATURAL  FACTORS 

IN  this  discussion  we  shall  consider  very  briefly 
the  natural  factors  which  help  in  the  control  of 
parasitic  insects. 

(a)  Beneficial  Predacious  Insects.  It  is  fortunate 
that  nature  always  provides  its  own  remedies.  If 
insect  pests  were  not  kept  in  check  by  natural  enemies 
the  trucker  who  does  not  spray  would  be  faced  by 
tremendous  odds  in  attempting  to  raise  crops.  The 
natural  and  beneficial  enemies  may  be  grouped,  first, 
into  parasites  which  develop  within  the  body  of  the 
host,  and  second,  predacious  or  those  which  feed 
externally. 

i.  Of  the  first  group  may  be  mentioned  a  small 
wasp-like  insect,  Lysiphlebus  testaceipes.  This  is  no 
doubt  an  important  parasite,  which  greatly  helps  to 
keep  the  green  Aphis  in  check.  Its  life  history  was 
originally  worked  out  by  Webster, r  and  may  be  briefly 
summarized  as  follows : 

A  mature  female  thrusts  her  ovipositor  into  the 
upper  side  of  the  Aphis  and  deposits  a  single  egg 

1  U.  S.  Dept.  of  Agr.  Bur.  of  Entomology  Bui.,  no,  1912. 

375 


376  Diseases  of  Truck  Crops 

within  its  body  (fig.  72  c-d).  The  egg  of  Lysiphlebus 
hatches  and  soon  begins  to  feed  on  the  vital  parts  of 
the  Aphis.  The  latter  gradually  ceases  activity  and 
finally  dies  and  becomes  mummified.  When  the 
larva  of  Lysiphlebus  reaches  maturity  and  pupates,  it 
emerges  through  a  circular  lid  cut  on  the  back  of  the 
dead  Aphis.  Lysiphlebus  is  not  active  at  tempera- 
tures below  56  degrees  F. 

2.  Of  the  parasites  which  feed  externally  on 
Aphids  may  be  mentioned  the  lady-bird  beetle,  of 
which  there  are  several  species.  These  actually  de- 
vour great  numbers  of  plant  lice.  Lady  beetles 
need  no  description,  as  they  are  well  known  to  all 
truckers.  There  are,  of  course,  other  important 
beneficial  insects  such  as  the  Syrphid  and  the  lace- 
winged  flies.  For  a  further  description  of  these  the 
reader  should  consult  Webster's  original  publication 
already  cited. 

(b)  Beneficial  Fungus  Parasites.  There  are  numer- 
ous species  of  fungi  which  from  an  economic  consider- 
ation are  very  important.  These  live  parasitically 
on  numerous  insect  pests  and  undoubtedly  greatly 
help  in  keeping  them  in  check.  Of  these  may  be 
mentioned  species  of  Empusa,  and  of  Acrostalagmus, 
which  live  on  Aphids  or  plant  lice.  Fungi  which 
belong  to  species  of  Aschersonia  are  parasitic  on  the 
white  fly.  The  fungus  Botrytis  rileyi  is  parasitic  on 
numerous  caterpillars.  The  fungus  Cordyceps  (fig. 
72  a-b)  contains  some  important  species  which  are 
parasitic  on  the  Harlequin  bugs  and  other  insect 
pests.  The  green  muscardine  fungus  Metarrhizium 


FIG.  72.     PARASITIZED  INSECTS.    TREATMENT  OF  FENCE  POSTS. 

a.  Cabbage  bug  parasitized  by  Cordyceps  nutans,  b.  cabbage  bug  parasitized  by 
Cordyceps  sobolifera  (a.  and  b.  after  Lloyd),  c.  watermelon  aphids  parasitized  by 
Lysiphlebus  testaceipes,  showing  circular  holes  on  the  backs  of  the  aphids  through 
which  parasite  emerged,  d.  a  female  of  L.  testaceipes  in  the  act  of  laying  her  eggs  in 
the  back  of  a  green  aphis  (after  Webster),  e.  Creosoted  post  after  a  period  of  service, 
i.  a  willow  post  treated  4  hours  in  hot  creosote  and  iq  hours  in  cold;  set  June  13, 
1005,  examined  November  I,  1914,  and  showing  practically  no  deterioration  after 
9/12  years'  service.  2.  A  split  soft  maple  post  treated  4  hours  in  hot  creosote  and 
10  hours  in  cold;  set  in  1905  and  examined  November  15,  1914.-  The  post  was  set 
below  the  creosote  line  and  some  decay  has  entered  beneath  the  creosote  shell,  j. 
A  s-inch  split  cottonwood  post  given  a  creosote  bath  treatment,  set  in  1905  and 
examined  in  1914.  The  post  shows  practically  no  decomposition  in  either  top  or 
bottom.  4.  An  8-inch  ash  post  split  in  half,  given  butt  creosote  treatment  of  6 
hours  in  hot  and  12  hours  in  cold,  set  1905  and  examined  in  November,  1914.  The 
creosoted  bottom  is  sound,  penetration  on  the  heart  wood  surface  was  less  than  in 
the  sap  wood.  The  heart  wood  portion  of  this  post  will  undoubtedly  give  away  first. 
The  untreated  top  is  in  excellent  condition.  5.  A  4^-inch  untreated  white  cedar 
post  after  standing  9*/£  years.  /.  A  small  treating  tank  in  operation,  (e.  and  /. 
after  McDonald). 


Natural  Factors  Controlling  Pests    377 

anisoplice  is  parasitic  on  numerous  grubs  and  beetles. 
Most  of  these  fungi,  however,  are  only  active  during 
warm  moist  weather  and  cannot  always  be  depended 
upon  with  certainty. 


CHAPTER  XXV 

TREATMENT  OF  FENCE  POSTS 

WHETHER  trucking  on  a  large  or  small  scale,  fence 
posts  are  always  used  to  protect  the  crops  from  pas- 
turing animals  or  undesirable  marauders.  In  buy- 
ing fence  posts,  the  aim  should  be  to  secure  those 
which  naturally  last  longest.  Posts  of  willow, 
cottonwood,  or  soft  maple  will  last  far  less  than  those 
of  red  cedar,  osage  orange,  or  the  mulberry.  Posts 
made  largely  of  sapwood  will  rot  much  faster  than 
those  made  of  heartwood.  All  posts,  before  being 
used,  should  be  rid  of  all  their  bark.  The  latter  usually 
harbors  insect  and  fungi  which  when  active  hasten 
destruction  or  decay.  In  order  to  preserve  the  life 
of  fence  posts  longest,  they  should  be  treated  with 
some  good  standard  preservative.  Creosote  is  the 
most  important  preservative  for  fence  posts  (fig.  72  e, 
I  to  5).  On  a  moderate  scale,  tanks  (fig.  72  f) 
four  feet  high,  three  feet  in  diameter,  and  capable 
of  holding  thirty-five  4>£-inch  posts  should  be 
used.  The  tank  is  raised  about  one  foot  above  the 
ground  to  provide  room  for  the  fire  box.  The  creo- 
sote is  poured  in  the  tank  and  the  posts  are  allowed 
to  remain  in  the  hot  preservative  for  a  period  of  from 
two  to  six  hours.  The  posts  may  then  be  allowed  to 

'378 


Treatment  of  Fence  Posts          379 

remain  in  the  tank  until  the  preservative  cools  off, 
or  it  is  immediately  transferred  to  another  tank  which 
contains  cold  creosote.  This  cooling  off  is  necessary, 
as  it  causes  a  contraction  of  the  remaining  air  and 
moisture  in  the  wood  structure.  This  causes  addi- 
tional preservative  to  be  drawn  into  the  wood. 

Fence  posts  may  be  treated  at  any  time  of  the  year. 
The  time  of  the  year  posts  are  cut  affects  only  the 
seasoning,  but  not  its  durability.  Posts  cut  in  the 
winter  are  more  difficult  to  peel.  Contrary  to  general 
belief,  winter  cut  posts  contain  more  moisture  and 
hence  require  longer  seasoning.  All  posts  to  be 
treated  must  have  all  the  bark  removed.  If  the 
posts  are  cut  in  the  spring,  the  peeling  of  the  bark 
is  very  easy.  Beveling  the  tops  of  treated  posts 
is  also  recommended.  This  is  especially  necessary 
when  the  posts  are  treated  at  the  butt  end  which 
is  stuck  in  the  ground. 


GLOSSARY 
A 

ACERVULI.  Small  groups  of  mycelial  tufts  upon  which 
fungus  spores  are  formed. 

^CIDIOSPORES.  Spores  of  the  rust  family  formed  in  an 
ascidium. 

^CIDIUM  (secium).  A  cup-shaped  body  in  which  are 
formed  the  spring  spores  of  certain  rust  fungi. 

AEROBE.    Organism  requiring  air,  more  especially  oxygen. 

AMMONIFICATION.  The  formation  of  ammonia  at  the 
expense  of  other  forms  of  nitrogen  compounds,  by 
the  action  of  microorganisms  upon  organic  sub- 
stances. 

AMMONIFIERS.  Micro6rganisms  capable  of  transforming 
nitrogen  compounds  into  ammonia. 

AMCEBOID.  Like  an  amoeba,  the  creeping  movement 
of  which  is  made  possible  by  appendage-like  bodies. 

ANTHERIDIUM.     The  male  sexual  organ  in  fungi. 

APICAL.  Terminal  formation  at  the  point  of  any  struc- 
ture. 

ARTHROSPORES.  Whole  vegetative  cells  of  either  bac- 
teria or  fungi,  which  by  a  thickening  of  their  walls 
become  resting  spores. 

ASCOSPORES.     Spores  formed  in  an  ascus. 

ASCUS.  A  sac-like  structure  in  which  the  winter  spores 
of  certain  fungi  are  formed. 


382  Glossary 

B 

BASIDIOSPORES.     Spores  formed  on  basidia. 
BASIDIUM.     A  straight  stick- like  spore  bearing  fungal 
thread. 


CANKER.     Definite  dead  area  in  the  bark  of  stems  or 

roots  of  plants. 

CAPITATE.     Possessing  a  head. 
CARBONACEOUS.     Dark  to  black  colored. 
CHLAMYDOSPORES.      Resting    spores    with    very    thick 

walls,  formed  within  mycelial  cells. 
CHLOROPHYLL.     Green  coloring  matter  in  leaves  of  the 

higher  plants. 

CHROMOGENIC.     Producing  color. 
CILIATE.     Fringed  with  hairs. 
COLUMELLA.     Sterile  axle  of  a  pillar-like  structure  within 

a  sporangium. 

CONIDIA.     Spores  formed  asexually. 
CONIDIOPHORE.     A  spore-bearing  fungal  stalk. 
CONSTRICTED.     Drawn  together  or  contracted. 
CORTEX.     Outer  bark. 
CUTICLE.     The  outermost  skin  of  plants. 
CYST.     Sac  or  cavity. 


DELIQUESCENT.     Dissolving  or  melting. 
DIFFUSE.     Loosely  spread. 
DILATED.     Enlarged. 

E 

ENDOSPORE.     Spore  formed  within  another  cell. 
ENTOMOGENOUS.     Living  on  insects. 


Glossary  383 

ENZYME.  An  organic  chemical  product  capable  of 
bringing  about  chemical  changes,  but  without  itself 
undergoing  any  change,  or  entering  into  the  final 
product. 

EXOSPORE.    Outer  covering  of  a  spore. 


FALCATE.     Sickle  shaped. 

FLAGELLA.  Whip-like  appendage  of  protoplasm  of  bac- 
teria and  swarm  spores. 

FUNGUS.  A  plant  of  very  low  order.  Its  mycelium  corre- 
sponds to  roots  and  reproduces  by  means  of  spores. 


GLAUCUS.     Sea  green. 
GONIDIA.     Algae-like  cells. 
GUTTULATE.     Drop-like. 


H 


HAUSTORIA.  Special  organs  of  a  fungus  used  for  attach- 
ment or  for  obtaining  food. 

HOST.     Any  plant  which  nourishes  a  parasite. 

HYALINE.     Translucent  or  colorless. 

HYPERTROPHIED.  Part  of  diseased  plant  abnormally 
enlarged. 

HYPH^E.     Thread-like  vegetative  part  of  a  fungus. 


INDURATED.     Hardened. 

INFECT.     To  cause  disease. 

INTERCELLULAR.     Growing  between  the  host  cells. 

INTRACELLULAR.     Growing  inside  the  host  cells. 


384  Glossary 


LENTICEL.  A  special  loose  corky  structure  in  plants 
intended  for  the  exchange  of  gases  of  the  air  and  the 
interior  of  the  plant. 

LESIONS.     A  definite  diseased  area. 


M 


MACROCONIDIA.     Large  conidia. 
MICROCONIDIA.     Very  small  conidia. 
MIDDLE  LAMELLA.     The  connecting  or  cementing  mem- 
brane between  any  two  cells  of  a  plant. 
MYCELIUM.     Vegetative  threads  or  hyphse  of  a  fungus. 
MYCOLOGY.     The  study  of  fungi. 

O 

OMNIVOROUS.     Attacking  a  large  variety  of  plants. 
OOGONIUM.     Female  sexual  organ  of  fungi,  containing 

one  or  more  oospheres. 
OOSPHERE.     Naked  mass  of  protoplasm  developing  into 

oospores  after  fertilization. 
OOSPORE.     Fertilized  oosphere. 


PAPILLATE.     Having  wing-like  structures. 

PARAPHYSES.     Sterile  filaments  found  in  some  fruiting 

forms  of  fungi. 
PARASITE.     An  organism  living  at  the  expense  of  another 

(the  host). 

PATHOGENE.     A  disease-producing  organism. 
PEDICILLATE.     Borne  on  a  stalk. 


Glossary  385 

PERITHECIUM.  A  flask-shaped  or  globose  sexual  fruiting 
body  containing  asci. 

PERITRICHIATE.     Flagella  all  over  the  surface. 

PIONNOTES.  An  effuse  conidial  stage  containing  a  maxi- 
mum of  conidia  and  a  minimum  of  aerial  mycelium. 

PLASMODIUM.  A  mass  of  naked  protoplasm  with  numer- 
ous nuclei  and  capable  of  amoeboid  motion. 

POLAR  FLAGELLA.  Flagella  borne  at  the  polar  ends  of  an 
organism. 

PROTOPLASM.     The  living  substance  of  any  plant  cell. 

PSEUDOPIONNOTES.     False  pionnotes. 

PSEUDOSTROMA.     False  stroma. 

PUSTULE.     A  blister  or  pimple. 

PYCNIDIA.  Sac-shaped  fruiting  bodies  of  a  fungus  in 
which  the  pycnospores  or  summer  spores  are  formed. 

PYCNOSPORES.  Summer  spores  of  certain  fungi  which 
are  formed  in  pycnidia. 


SCLEROTIA.  Compact  masses  of  mycelium  in  a  dormant 
state.  These  help  to  carry  the  fungus  over  un- 
favorable weather  conditions. 

SEPTUM.  Any  partition  between  two  cells  in  the  same 
fungus  filament. 

SET^E.     Bristle-shaped  bodies. 

SOIL  FLORA.     Bacterial  or  fungus  growth  in  a  soil. 

SORUS.     Heap  of  spores. 

SPORANGIOPHORE.     Stalk-bearing  sporangium. 

SPORANGIOSPORES.     Spores  formed  in  a  sporangium. 

SPORANGIUM.     Free  non-sexual  bearing  spore  sac. 

SPORES.     Seed  of  bacteria  or  fungi. 

STOMATA.  Minute  openings  in  the  stems,  leaves,  or  fruits 
of  plants  which  serve  as  a  medium  of  exchange  of 
gases. 


386  Glossary 

STROMA.     A  spore-bearing  cushion  composed  of  mycelium 

and  sometimes  of  host  tissue. 
SWARM  SPORES.     Spores  possessed  with  the  power  of 

motility. 


TELEUTOSPORES  (xELio SPORE s) .     Resting  or  winter  spores 
of  certain  rust  fungi. 

U 

UREDOSPORES.     Summer  spores  of  certain  rust  fungi. 

V 

VESICULAR,     Composed  of  vessels. 
VISCID.     Sticky. 


ZOOGLE^.     Colony  embedded  in  a  gelatinous  bed. 
ZOOSPORANGIA.     Sporangia  which  produce  zoospores. 
ZOOSPORE.     A  motile  spore. 


INDEX 


Abbot,  J.  B.,  30. 
Acid  sick  soils,  25  et  seq. 
Acrostalagmus  panax,  113. 
Actinomyces,  6. 

chromogenus,  317. 

attacking  beets,  120. 

attacking  radish,  209. 

Alkali  sick  soils,  34  et  seq. 
Allard,  H.  A.,  84. 
Allium  cepa,  285. 

schoenoporasum,  284. 

Alphano  Humus  Co.,  20. 
Alternaria  brassica,  196. 

var.  nigrescens,  2,23. 

-—  panaXj  1 14. 

Ammoniacal  copper  carbonate, 

366. 

Ammonification,  14. 
AnthericUum,  n. 
Aphis  gossypii,  233. 
Apium  graveolens,  355. 
Arthur,  J.  C.,  117,  138. 
Artichoke,    Globe,    diseases   of, 
139  et  seq. 

Leaf  spot,  139. 

Jerusalem,  diseases  of,  137 

et  seq. 

Downy  mildew,  138. 

Leaf  blotch,  138  et  seq. 

Rust,  138. 

Ascochyta  armor  aci&,  205. 

hortprum,  302. 

pisi,  277. 

Asparagus  (officinalis),  280. 

diseases,  279  et  seq. 

Leopard  spot,  280. 
Rust,  280. 


Asparagus,  resistant  to  rust,  283. 

rust,  natural  enemies,  283. 

Atkinson,  G.,  43. 
Available  nitrogen,  elaboration 
of,  13. 


B 


Bacillus,  4. 

Bacillus  carotovorus,  192. 

: attacking  onions,  285. 

attacking  salsify,  146. 

fluorescens  liquefaciens,  14. 

putridus,  14. 

lathy 'ri,  261. 

on  cowpea,  270. 
phytopthorus,  316. 

melonis,  221. 

mesentericusvulgatus,  14,23. 

mycoides,  14,  23. 

pestifer,  23. 

pro  tens  vulgaris,  14. 

ramosus,  23. 

subtilis,  23. 

tracheiphillus,  attaching  cu- 
cumber, 229. 

Bacteria,  distribution  in  soil,  6. 

forms,  4. 

influence  of  depth  of  cul- 
tivation, 8. 

number  influenced  by  man- 
ure, 9. 

relationship  to  function  of 

soil,  5. 

Bacterium  teutlium,  118. 

Balm  diseases,  256. 
Leaf  spot,  256. 
Rust,  256. 

Barus,  M.  F.,  265. 


388 


Index 


Bean  diseases,  260  et  seq. 

Anthracnose,  263. 

Blight,  260. 

Damping  off,  261. 

Downy  mildew,  261. 

Powdery  mildew,  262. 

Rust,  262. 

Sclerotinia  rot,  263. 

Stem  anthracnose,  263. 

Streak,  261. 
Beattie,  W.  R.,293. 
Beet  diseases,  117  et  seq. 

Crown  gall,  118,  119. 

Damping  off  and  root  rot, 

122,  123. 

Downy  mildew,  123. 

Drop,  124. 

Leaf  spot,  126,  127. 

Leaf   spot   and   heart   rot, 
125,  126. 

Root  knot,  129,  130. 

Root  rot,  128. 

Root  tumor,  121,  122. 

Scab,  120-121. 

Soft  rot,  1 1 8. 

Tuberculosis,  120. 

Water  core  spots,  117. 

White  rust,  123. 
Beneficial  fungi,  376. 
Bessey,  E.  A.,  51. 
Beta  vulgaris,  117. 
"Black  leaf  40,"  368. 
Blinn,  P.  K.,  224. 
Blossom  drop,  82,  83. 
Bordeaux  mixture,  364. 
Branch,  G.  V.,  226. 
Brassica  Japonica,  208. 

oleracea,  186. 

var.  acephala,  207. 

var.  botrytis,  202. 

rapa,  214. 

Bremia  lactuc®,  141. 
Brown,  N.  A.,  140. 


Cabbage  diseases,  186  et  seq. 
Black  leg  or  foot  rot,  195. 
Black  mold,  196. 
Black  rot,  190. 


Club  root,  1 86. 

Damping  off,  193. 

Downy  mildew,  194. 

Drop,  194. 

Leaf  spot,  196. 

Root  knot,  199. 

Soft  rot,  192. 

White  rust,  193. 

Wilt  or  yellows,  197. 

storage  decays,  199  et  seq. 

Cantaloupe,  225. 

blight  resistant,  225. 

care  in  shipping,  225  et  seq. 

diseases,  219  et  seq. 

Anthracnose,  223. 

Bacterial  wilt,  219. 

Cercospora  leaf  spot,  224. 

Cladosporium  mold,  224. 

Downy  mildew,  221. 

Leaf  blight,  223. 

Mycosphaerella  wilt,  222. 

Phyllosticta  leaf  spot,  224. 

Powdery  mildew,  222. 

Root  knot,  225. 

Soft  rot,  221. 

Southern  blight,  225. 

spraying,  232. 

Capnodium,  238. 

Carbon,  transformation  of,  13. 

Carrot  diseases,  354. 

Root  rot,  354. 

Soft  rot,  354. 
Carum  petroselinum,  357. 
Catnip  diseases,  257. 

Leaf  spot,  257. 

Stem  rot,  257. 
Cauliflower  diseases,  202  et  seq. 

Bacterial  leaf  spot,  202. 

Ring  spot,  204. 
Causes  of  diseases  in  crops,  71 

et  seq. 
Celery  diseases,  355  et  seq. 

Early  blight,  357. 

Late  blight,  355. 

Leaf  spot,  355. 

Rust,  355. 

Soft  rot,  355. 
Cercospora  apii,  357,  358. 

armoracicB,  207. 

canescens,  269. 


Index 


389 


Cercospora  capsisi,  304. 

citrullina,  243. 

cruenta,  271. 

cucurbitce,  224. 

dolichi,  271. 

hibisci,  295. 

Chive  diseases,  284. 
Choanophora  cucurbitarum,  235. 
Chrysophylyctis    endobioticum, 

319. 

Citron  diseases,  234. 
Citrullus  vulgaris,  234  et  seq. 
Cladosporium  fulvum,  350. 

macrocarpum,  134. 

sp.f  284. 

Clinton,  G.  P.,   122,  124,   147, 

215,  284,  323. 
Coccus,  4. 

Cochleaia  armor acia,  204. 
Colletotrichum       atramentarium, 

325,  326 

caulicolum,  266. 

Higginsianum,  214. 

nigrum,  303. 

phomoides,  348. 

Combination  sprays,  367. 
Conidia,  12. 
Conn,  J.  H.,  6. 
Contact  poisons,  363. 
Convulvulus  batatas,  151. 
Cooley,  B.  A.,  368. 
Corticium  vagum,  128. 
Cowpea  diseases,  270  et  seq. 

Angular  leaf  spot,  271. 

Powdery  mildew,  271. 

Rust,  271. 

Streak,  270. 

Wilt  or  Yellows,  270. 
Crop  rotation,  272. 
Cucumber  diseases,  228  et  seq. 

Angular  leaf  spot,  229. 

Anthracnose,  232. 

Bacterial  wilt,  229. 

Damping  off,  230. 

Downy  mildew,  230. 

Mosaic,  228. 

Powdery  mildew,  230. 

Root  knot,  232. 

spraying,  232. 

Cucumis  sativus,  228. 


Ciicumis  melo,  219. 
Cucurbita  maxima,  234. 

moschata,  234. 

pepo,  234. 

Cutworms,  52. 

Cystopus  candidus,  attacking  rad- 
ish, 211. 

on  horseradish,  205. 

ipom<z<z-panduran<z,  155. 

portulacecz,  299. 

Cystospora  batatas,  152. 


D 


Damping  off,  42  et  seq. 

Darluca  filum,  284. 

Daucus  carota,  354. 

Denitrification,  24. 

Denitrified  soils,  23. 

Diabrotica  vittata,  220. 

Diaporthe  battis,  157,  159. 

Didlake,  M.,  20. 

Didymella  catarice,  257. 

Diplodia  herbarum,  258. 

herbicola,  257. 

tubericola,  16=5. 

,  attacking  watermel- 
on, 239. 

Diseases  of  a  mechanical  nature, 
72  et  seq. 

of  an  unknown  origin,  83 

et  seq. 

due  to  bacteria  or  fungi, 

86  et  seq. 

Dodder,  90,  91. 

Doryland  Ch.,  8. 

Drought  injury,  78. 

Duggar,  B.  M.,  128,  298. 

Durst,  C.  E.,  233. 


Edgerton,  C.  A.,  264. 
Edson,  H.  A.,  209. 
Eggplant  diseases,  300  et  seq. 

Anthracnose,  302. 

Damping  off,  301. 

Fruit  rot,  301. 

Root  knot,  303. 

Southern  blight,  303. 


390 


Index 


Eggplant  diseases — Continued 
Southern  wilt,  301. 
Stem  anthracnose,  303. 

Elliott,  J.  A.,  154. 

Enlows,  E.  M.,  229. 

Entyloma  Ellisii,  133. 

Erysiphe  cichoracearum,  232. 

galeopsidis,  258. 

polygoni,  216. 

,  on  bean,  262. 

,  on  cantaloupe,  222. 


Family  Agaricaceae,  103  et  seq. 

Araliaceffi,  108  et  seq. 

Chenopodiaceae,  1 16  et  seq. 

Composite,  137  et  seq. 

Convolvulaceae,  151  et  seq. 

Cruciferae,  185  et  seq. 

Cucurbitaceae,  218  et  seq 

Gramineas,  250  et  seq. 

Labiatae,  255. 

Liliaceae,  279  et  seq. 

Malvaceae,  295  et  seq. 

Portulacaceae,  299. 

Solanaceae,  300  et  seq. 

Umbelliferae,  254  et  seq. 

Fence  post  treatment,  378. 
Fertility  of  soil,  16,  17 
Fisher,  O.  S.,  31. 
Fleet,  W.  V.,  255. 
Formaldehyde,  treatment  of  soil, 

53,  54- 

Freiberg,  G.  W.,  84. 
Frost  injury,  74,  75. 

prediction,  76,  77. 

protection,  77,  78. 

Fuligo  violacea,  152. 

Fungicides,  363. 

Fungi,  structure  and  life  history, 

10. 
Fusarium  batatatis,  47,  157,  170. 

citrulli,  244. 

conglutinans,  197. 

cucurbittz,  237. 

eumartii,  330. 

hyperoxysporum,  47  et  seq. 

ly  coper  sici,  351. 

niveum,  244. 


Fusarium  orthoceras,  352. 

oxysporum,  327,  352. 

Poolensis,  244. 

radicicola,  329. 

trichothecioides,  330. 

•  tuberivorum,  331. 


Garden  pea,  275. 

diseases,  273  et  seq. 

Pod  spot,  276. 

Root  knot,  278. 

Root  rot,  278. 

Septoria  leaf  spot,  278. 

Stem  blight,  273. 

Thielavia  root  rot,  275. 
Garman,  H.,  20. 
Gilbert,  W.  W.,  74. 
Gilman,  J.  C.,  198. 
Ginseng,  no,  in,  113. 
diseases,  108  et  seq. 

Acrostalagmus  wilt,  113, 114 

Alternaria  blight,  114. 

Black  rot,  110,  in. 

Bordeaux  injury,  115. 

Damping  off,  108. 

Downy  mildew,  ro8,  109. 

Fiber  rot,  in,  112. 

Leaf  anthracnose,  113. 

Papery  leaf  spot,  115. 

Root  knot,  115. 

Stem  anthracnose,  112. 

White  rot,  1 10. 
Gleosporium  melongena,  302. 
Glomerella  piper ata,  303. 
Grossenbacher,  J.  G.,  222. 

H 

Hail  storm,  73,  74. 
Halstead,  B.  D.,  125. 
Harding,  H.  A.,  191. 
Harris,  F.  S.,  35. 
Harter,  L.  L.,  199,  301. 
Hawkins,  321. 
Headen,  W.  P.,  16,  24. 
Heald,  F.  D.,  139,  266. 
Healthy  host  and  its   require- 
ments, 63  et  seq. 


Index 


Healthy  soil  flora,  nature  and 

function,  12. 
Helianthus  annuus,  148. 

tuber osus,  137. 

Heterodera  radicicola,  48,  52,  332. 
attacking     cabbage, 

199. 

attacking  beets,  129. 

attacking  lettuce,  146. 

attacking  sweet  pota- 
to, 176. 

Heterosporium  variabile,  134. 
Hibiscus  esculentus,  295. 
Hicks,  G.  A.,  96.  ' 
Higgins,  B.  BM  214. 
Hopkins,  G.  G.,  31. 
Horehound  diseases,  258. 

Leaf  spot,  258. 

Powdery  mildew,  258. 
Horseradish  diseases,  204  et  seq. 

Leaf  spot,  207. 

Macrosporium  black  mold, 
206. 

Root  rot,  205. 

Shot  hole,  206. 

White  mold,  206. 
Humbert,  J.  G.,  55. 
Humphrey,  J.  E.,  232. 


Insecticides,  362. 
Iron,  changes  of,  15. 
Irrigation,  methods  of,  67  et  seq. 
Isariopsis  griseola,  269. 
Istvanffi,  G.  De,  143. 

J 

Jamieson,  C.  O.,  331. 
Johnson,  J.,  57,276. 

T.,  320,  347. 

Jones,  L.  R.,  74. 


Kale  diseases,  207,  208. 
Koch,  Robert,  4. 


Lactuca  saliva,  140. 
Lady  beetles,  376. 
Leeuwenhoek,  Anton  van,  4. 
Lettuce  diseases,  140  et  seq. 

Bacterial  blight,  140. 

Cercospora  leaf  spot,  145. 

Downy  mildew,  141. 

Gray  mold,  142. 

Leaf  spot,  144. 

Lettuce  drop,  143. 

Root  knot,  146. 

Rosette,  146. 

Shot  hole,  145. 
Levine,  E.,  347. 
Lightning  injury,  74,  75. 
Lima  bean  diseases,  267  et  seq. 

Blight,  267. 

Downy  mildew,  267. 

Leaf  blotch,  269. 

Leaf  spot,  269. 

Pod  blight,  268. 

Powdery  mildew,  268. 

Root  rot,  269. 

Rust,  268. 

Texas  root  rot,  269. 
Lutman,  B.  F.,  318. 
Lycopersicum  esculentum,  339. 
Lysiphlebus  testaceipes,  375. 

M 

McClintock,  J.  A.,  263. 
McCulloch,  L.,  202. 
McKay,  M.  B.,  127. 
Macrosporium    herculeum,    206, 
217. 

parasiticum,  290. 

porri,  290. 

solani,  325. 

sp.,  304. 

Malnutrition,  80  et  seq. 
Manns,  T.  F.,  99,  195. 
Marrubium  vulgare,  258. 
Marsonia  perforans,  145. 
Meier,  F.  C.,  239. 
Melanconium  Tisdale,  349. 
Melhus,  T.  E.,  212,  323. 
Meliotus  alba,  20. 


392 


Index 


Meliotus  denticulata,  20. 

lupulina,  20. 

Melissa  officinalis,  256. 
Mentha  virides,  258. 
Merrill,  L.  A.,  65. 
Methods  of  control,  361. 
Mint  diseases,  258. 
Monilochates  infuscans,  168. 
More,  C.  T.,  226. 
Morse,  W.  J.,  316. 
Mosaic,  83  et  seq. 
Muck  or  peat  soils,  34  et  seq. 
Mushroom  diseases,  103  et  seq. 

Bacterial  spot,  103,  104. 

The  Mycogone  disease,  103 

et  seq. 

Mustard  diseases,  208. 
Mycogone  perniciosa,  104,  105. 
Mycospharella  brassicola,  204. 
citrulina,  22. 


N 


Nematospora  lycopersici,  345. 
Nepeta  cataria,  257. 
Niter-sick  soils,  24. 
Nitrification,  14. 
Nitrobacter,  14. 
Nitrogen  fixation  from  air,  18. 
— —  maintaining  supply,  17. 
Nitrosococcus,  14. 
Nitrosomonas,  14. 

O 

O'Gara,  P.  J.,  324. 
Okra  diseases,  295  et  seq. 

Leaf  spot,  295. 

Root  knot,  298. 

Root  rot,  297. 

Texas  root  rot,  297. 

Wilt,  296. 

Olpidium  bras  sices,  193. 
Onion  diseases,  285  et  seq. 

Anthracnose,  289. 

Black  mold,  290. 

Black  neck,  290. 

Blight,  286. 

Bulb  rot,  290. 

Damping  off,  286. 


Downy  mildew,  286. 

Pink  root,  291. 

Rust,  289. 

Sclerotium     rot    or    black 
neck,  290. 

Smut,  288. 

Soft  rot,  285. 

storage,  292  et  seq. 

Oogonia,  43. 

Oogonium,  n,  43. 

Orton,  W.  A.,  232,  273,  327. 

Ozonium   omnivorium   attacking 

okra,  297. 

attacking  sweet  pota- 
to, 175. 


Pammel,  L.  H.,  46,  123. 
Parasitic  fungi,  10. 

soil  Fusaria,  46,  47. 

Parsley  diseases,  357. 

Drop,  357. 

Late  blight,  357. 
Parsnip  diseases,  357. 

Early  blight,  357. 

Root  rot,  357. 
Pastinaca  sativa,  357. 
Penicillium  expansum,  n. 
Pepper  diseases,  303  et  seq. 

Anthracnose,  303. 

Black  anthracnose,  303. 

Fruit  rot,  304. 

Leaf  spot,  304. 

Southern  blight,  305. 
Peppermint  diseases,  258. 
Perithecium,  12. 
Peronflsporaeffusa,  131,  132. 
parasitica     attacking    cab- 
bage, 194. 

schachtii,  123. 

schleideni,  286. 

Pestalozziafunerea  attacking  gin- 
seng, 113. 

Phaseolus  vulgaris,  260. 
Phoma  beta,  125. 

destruction.  346. 

napobrassiccc,  215. 

oleracea,  195. 

solani,  324. 


Index 


393 


Phoma  subcircinata,  268. 
Phomosis  vexans,  301. 
Phosphates,  changes  of,  15. 
Phyllosticta  apii,  355. 

batatas,  164. 

chenopodii,  133,  134. 

cucurbitacearum,  224. 

Physiological  diseases,  80  et  seq. 
Phythium  de  Baryanum,  42,  44, 

193- 

attacking  beet,  122. 

Phytophthora  cactorum,  108. 

infestans,    late    blight    of 

Irish  potato,  322. 
late  blight  of  tomato, 

343- 

phaseoh,  267. 

terrestria,  344. 

Pisum  sativum,  273. 
Plasmopora  Halstedii,  138,  148. 
Plenodomus  destruens,  159. 
Points  to  remember,  366. 
Pool  Venus,  127. 
Poor  seed,  92,  97. 
Potassium,  changes  of,  15. 

sulphide  of,  369. 

Potato  diseases,  306  et  seq. 

Anthracnose,  324. 

Arsenical  injury,  313. 

Black  heart,  311. 

Black  leg,  316. 

Black  rot  or  jelly  end  rot, 

329- 

Black  wart,  319. 
Common  scab,  317. 
Curly  dwarf,  309. 
Early  blight,  322. 
Fusarium  wilt,  327. 
Hollow  heart,  312. 
Internal     brown     spotting, 

310. 

Late  blight,  322. 
Leaf  roll,  308. 
Melters  or  leak,  321. 
Mosaic,  312. 
Net  necrosis,  311. 
Phoma  rot,  324. 
Powdery  dry  rot,  330. 
Powdery  scab,  314. 
Pox  or  pit,  313. 


Root  knot,  332. 
Rosette,  331. 
Silver  scurf,  326. 
Southern  blight,  332. 
Southern  wilt,  317. 
Spindling  sprout,  310. 
Stem  end  rot,  329. 
Tip  burn,  312. 

-  diseases,  field  control,  335. 
--  storage  rots  control,  333. 
Predacious    insects,    beneficial, 

375- 

Pseudomonas  beticola,  120. 
--  campestris,  190,  191,  205. 
--  attacking  radish,  208. 
---  attacking  turnip,  214. 

-  fluorescens,  103,  104. 

-  lachrymans,  229. 
--  maculicola,  202,  203. 

-  pisi,  273. 

--  radicicola,  18  et  seq. 
--  solanacearum,  attacking  to- 
mato, 342. 

-  Stewarti,  251. 

-  tumefaciens,  attacking  beets, 
118. 

-  viridilividum,  140. 
Pseudoperonospora  cubensis,  230. 
Puccinia  alii,  289. 

-  asparagi,  280. 


-  helwnthi,  149. 
--  attacking     Jerusalem 

artichoke,  138. 

-  tragopogoni,  148. 
Purslane  diseases,  299. 
Pycnidium,  12. 


Radish  diseases,  208  et  seq. 

Black  rot,  208. 

Club  root,  208. 

Damping  off,  209. 

Downy  mildew,  211. 

Root  knot,  214. 

Root  rot,  214. 

Scab,  209. 

White  rust,  211. 
Rainstorms,  73. 


394 


Index 


Ramularia  armoracia,  206. 

cynarce,  138. 

Rand,  F.  V.,  229. 
Rankin,  W.  H.,  no. 
Raphanus  sativus,  208. 
Readhimer,  J.  E.,  31. 
Reid,  H.  L.,  134,  138. 
Resin,  370. 

Resistant  varieties,  373. 
Rheosporangium   aplianiderma- 

tum,  209. 

Rhizoctonia  solani,  44. 
Rhizopus  nigricans,  156,  158. 

attacking  squash,  236. 

the  cause  of  leak,  32 1 . 

Roasting  or  pan  firing,  56. 

Rogers,  S.  S.,  356. 

Root  knot,  48  et  seq. 

Root  rot,  caused  by  Rhizoctonia 

solani,  45,  46. 
Rosenbaum,  J.,  109,  no,  314. 


Sackett,  W.  G.,  24. 
Salsify  diseases,  146  et  seq. 

Rust,  148. 

Soft  rot,  146. 

Southern  blight,  148. 

White  rust,  147. 
Sal  soda,  370. 

Sanitary  environment,  69,  70. 
Sarcina  lutea,  14. 
Schneider,  A.,  345. 
Schrenk,  H.  von,  203. 
Sclerotinia  libertiana,  45. 

attacking  bean,  263. 

attacking  beet,  124. 

attacking  cabbage, 

194- 

attacking  ginseng,  1 10. 

— —  panacis,  no. 

Sclerotium  bataticola,    157,    173, 

174- 

cepivorum,  290. 

Rolfsii,  44. 

attacking  cantaloupes, 

225. 
attacking  peppers, 

305. 


Sclerotium  Rolfsii,  attacking 
sweet  potatoes,  174. 

attacking  watermelon, 

247. 

Seed,  age  of,  92. 

cultural  conditions,  92,  93  . 

fertilizer  effect,  95,  97. 

storage  conditions,  94. 

testing,  95. 

treatment  against"  insects, 

97- 

treatment  with  formalde- 
hyde, 99. 

weight  and  color,  93,  94. 

Selby,  A.  D.,  55,  291. 

Septoria  bataticola,  165. 

consimilis,  144. 

lactucce,  144. 

lycopersici,  347. 

melissa,  256. 

nepetcB,  257. 

pisi,  278. 

Shamel,  A.  D.,  54. 

Sherbakoff,  C.  D.,  331,  344. 

Sick  soil,  treatment,  53. 

Sirrine,  F.  A.,  282. 

Smith,  E.  F.,  119,  190,  251. 

E.  W.,230. 

R.  E.,  281. 

Smoke  injury,  78  et  seq. 

Soft  rot,  236. 

Soil  flora,  action  on  mineral  sub- 
stances, 14. 

Solonum  tuberosum,  306. 

Spearmint  diseases,  258. 

Sphcsrella  pinodes,  276. 

Spharonema    fimbriatum,     160, 

173- 

Spinach  diseases,  130  et  seq. 
Anthracnose,  132. 
Black  mold,  134. 
Downy  mildew,  131,  132. 
Leaf  spot,  134,  136. 
Malnutrition,  130,  131. 
Phyllosticta  leaf  blight,  133, 

134- 

White  smut,  133. 
Spinacia  oleracea,  130. 
Spondylocladium  atrovirens,  324, 
326. 


Index 


395 


Spraying,  361. 

machines,  370. 

principles  involved,  370. 

Squash  diseases,  234  et  seq. 
Anthracnose,  237.^ 
Bacterial  wilt,  234. 
Fruit  rot,  235. 
Leaf  spot,  237. 
Powdery  mildew,  237. 
Root  knot,  238. 
Root  rot,  238. 
Soft  rot,  236. 
Wilt  or  yellows,  237. 
Steaming  sick  soil,  54. 
Stevenson,  J.  A.,  146. 
Stewart,  F.  C.,  128,  285. 

-F.G.,25i. 
Stickers,  370. 
Stock  solutions,  364. 
Stomach  poisons,  362. 
Stone,  G.  E.,  93. 

R.  E.,  277. 

Subirrigation,  67,  68. 
Sulphur,  367. 
Sunflower  diseases,  148. 
Downy  mildew,  148. 
Rust,  149. 
Surface  or  spray  irrigation,  68, 

69. 

Sweet  potato  diseases,  151  et  seq. 
Black  rot,  160. 
Charcoal  rot,  173. 
Cottony  rot,  174. 
Dry  rot,  159. 
Foot  rot,  159. 
Java  black  rot,  165. 
Phyllosticta  leaf  blight,  164. 
Ring  rot,  158. 
Root  knot,  176. 
Septoria  leaf  spot,  165. 
Slime  mold,  152. 
Soft  rot,  156. 
Soil  rot,  152. 
Soil  stain  or  scurf,  168. 
Texas  root  rot,  175. 
Trichoderma  rot,  167. 
Vine  wilt  or  yellows,  170. 
White  rust,  155. 

methods  of   control, 

176  et  seq. 


Taubenhaus,  J.  J.,  160  et  sea. 

Temple,  J.  C.,  9. 

Thick  sowing,  effect  on  damping 

off,  57. 

Thielavia  basicola  attacking  gar- 
den pea,  275. 

attacking  ginseng,  1 1 1 . 

attacking  horseradish, 

205. 

Tmsley,  J.  D.,  37. 
Tolaas,  A.  S.,  103. 
Tomato  diseases,  339  et  seq. 

Anthracnose,  348. 

Blossom  end  rot,  340. 

Buckeye  rot,  344. 

Damping  off,  343. 

Fruit  rot,  346. 

Hollow  stem,  339. 

Late  blight,  343. 

Leaf  spotf>  347. 

Melanconium  rot,  349. 

Mosaic,  3^1. 

Rhizoctonia  fruit  rot,  353. 

Southern  wilt,  342. 

Sunburn,  341. 

Yeast  rot,  345. 

Yellow  blight,  352. 
Tragopogon  porrifolius,  146. 
Trichoderma  koningi,   167. 

lignorum,  167. 

Tubercularia  persicina,  284. 
Turnip  diseases,  214  et  seq. 

Anthracnose,  214. 

Black  rot,  214. 

Club  root,  214. 

Macrosporiumleaf  spot,  217. 

Phoma  rot,  215. 

Powdery  mildew,  216. 


U 


Uredinales,  10. 
Urocystis  cepulce,  288. 
Uromyces  appendiculatus,  262. 
Urophlyctis  leproides,  121. 


396 


Index 


Veihmeyer,  F.  J.,  105. 
Vermicular ia  circinans,  289. 

dematium,  112. 

Verticillium  albo-atrum,  326. 

W 

Ward,  M.,  43. 

Water,  need  of  plants,  64,  67. 

Watermelon  diseases,  238  et  seq. 

Anthracnose,  240. 

Bacterial  wilt,  238. 

Blossom  end  rot,  247. 

Cercospora  leaf  spot,  243. 

Downy  mildew,  238. 

Fruit  rot,  247. 


Honey  dew  or  sooty  mold, 
238. 

Malnutrition,  238. 

Mycosphaerella  wilt,  239. 

Powdery  mildew,  238. 

Root  knot,  246. 

Stem  end  rot,  239. 

Vine  wilt  or  yellows.  244. 
Whetzel,  H.  H.,  no,  287 
White  grubs,  52. 
Whitney,  M.,  64. 
Widtsoe,  J.  A.,  65. 
Wind  storms,  72,  73. 
Wire  worms,  52. 
Wolf,  F.  A.,  139,  235. 
Wollenweber,  H.  W.,  331. 


Zea  mays,  250. 


f  ~ 


U.C.  BERKELEY  LIBRARIES 

C02735M312 


